It's all in the people.
Of course, the very best part of this workshop was the people who attended it. It's amazing to get people from NVDA, JAWS and ChromeVox into a room for a few days. It's even better when you have people from MathJax, MathLive, Desmos in the same room. It gets even better when you have publishing experts from Wiley and Pearson on board. It's incredibly much better to have the vast expertise of people such as T.V. Raman and Joanie Diggs there. But for me, the most thrilling was the educators in the room. They are the key and without them we are all lost. And I'm the first to admit the workshop didn't serve them well enough. Even more importantly, at future workshops we need to get students in the room as well. Because what the hell are we doing without them.
In extension, this is a compliment to AIM's workshop design. Providing funding not only for a workshop but for everyone's travel and accommodation was excellent but also crucial. We would never have been able to get all these people in a room. This is the right way to hold workshops, especially when inclusiveness is a huge issue.
There's a particular limitation of today's accessibility landscape: we cannot specify separate textual alternatives for voice and Braille.
Generally, not having separate streams for voice and Braille does not seem like a huge problem. As long as all accessibility needs are covered by a fixed set of standard elements that are designed for both aural and tacticle interfaces, then assistive technologies can reliably implement a split in the stream, i.e., present separate voice and Braille streams from that. For example, if you have a dedicated button element, it can represented as a btn
contraction on a Braille display and voiced as Button.
As usual, not all things can be covered by standards. Say your button is is used as a control in a game then you may want to augment the button's accessible name to include the action. So if the button opens a selection of planets to travel your to in your game, then you may want to have this voiced as planet. You can do that of course and then you might get a voicing of planet; button and something akin to pln btn
on a Braille display.
Unfortunately, you might find yourself in a situation where you need to prevent the addition of button in the voicing because it may be problematic for your aural users, e.g., users with learning disabilities may find it to be distracting noise. But now how do you identify the button on a Braille display?
For equation layout, the situation is much like that final situation. In many countries, specialized Braille formats such as Nemeth, UEB, or Marburg have been developed to represent equation layout in Braille. These are well established and there are not too difficult to create. But they differ considerably from what you would might want to render aurally (and visually). In fact, since most precede the web, they try to capture (simplified) visual layout, including all the ambiguities we face there.
For me, the greatest positive experience of the workshop was to see the group assess the problem, come to an agreement that it needs a solution, add it to the ARIA tracker, build demos and even see NVDA whip up a first implementation that we could explore by the end of the week.
This was huge.
And yet, it is the easy part. Now the long road towards a proper standard with widespread implementations lies ahead.
I brought my favorite problem to the workshop  deep arialabel
s and I was not disappointed.
Assistive technologies for equation layout (in particular for MathML) have to apply heuristics (read: guess) the semantics of an expression so that they can generate meaningful nonvisual representations. This is a problem because heuristics that are hard coded into an external tool such as screenreaders cannot be altered by standard means, leaving authors without adequate means to ensure the quality of their content. (If a screenreader voices every superscripted 2 as squared and you have no way of changing that, then you're screwed.)
More importantly, since equation layout is, ultimately, only visual, a perfectly correct representation in HTML is as span
s, i.e., there are no semantics. Finally, ARIA (naturally) does not have a dictionary of equation layout terminology (let alone mathematical or scientific terminology) to use  a) because all past dictionary based approaches have failed and b) such a dictionary would have to be extensible (read: infinite) which ARIA, so far, does not really want to be (roledescription
notwithstanding).
So the pragmatic answer is: you'll just have to do it yourself and use deep arialabel
s: you override every single accessible name computation by slapping a fixed label to things. Because, ultimately, this is how we read equational content  with words.
The trouble is that it's easy to add a single arialabel
at the root but it is hard to provide an explorable structure that provides a decent user experience. You'll want to provide labels at the leaf level but the state of ARIA prevents those from adequately building up an explorable tree. (And we're not even talking about refinements such as providing summaries and structural and positional information during exploration.)
At the workshop, David Tseng from Google's ChromeVox team, Volker Sorge from Speech Rule Engine and Davide Cervone from MathJax sat down nd build a first demo that tries two things
ariaowns
attributeariaactivedescendant
manipulationsThis is, simply put, a fantastic step forward.
The approach builds on existing parts of ARIA and identifies reasonable, incremental improvements to it. It raises important questions on general exploration, e.g., how is there a generic ariatable
walker in every screenreader but not some basic ariatree
walker (such as breadth or depth first)?. And yet it pragmatically builds an unobtrusive solution anyway that works at 60FPS. It works with any markup, in particular any approach using CSS or SVG markup. And to top it off, it leverages existing opensource tool to enrich preexisting content. And while it shows just how far ahead MathJax and Speech Rule Engine are, this approach is transparent and easily used by any other equation layout library.
In terms of UX, this is also a critical step forward. The approach is should be able to provide a seamless an interaction for visual and nonvisual users alike, in synchronization. Effectively, it pushes MathJax's Accessibility Extensions from client to serverside, requiring minimal JavaScript (just a keyboard event listener) to expose the content, without live region hacks, and with a solid nonJS fallback. It provides a clear path for making even that bit of JS obsolete through natural improvements to ARIA. It opens a path to finally get rid of the horrible hackery such as JAWS did back in the day, manipulating IE's DOM to manipulate MathJax, or Texthelp is doing today by injecting JS on the client (yuck!, and also badly failing when contentsecurity is in place).
Even better, if you combine it with the previous part (exposing specialized Braille which SRE can soon produce), then this would immediately become the by far best, universal rendering of equation layout on the web: robust, highquality, customizable, precise. And it is a solution that will only get better as standards evolve while leaving the full control with the author (with or without aid of heuristics at authoring time).
I'll dig into this more some other time but admittedly, I'm pretty excited.
You can find the organizers' report at aimath.org but you can take one thing away: It's looking very good for accessible equation layout on the web these days. And it will only get better.
If we can continue these workshops, things will move faster for everyone. And maybe, just maybe, we can even finally move on to actual mathematics (and other STEM content) on the web.
]]>We determine the consistency strength of determinacy for projective games of length $\omega^2$. Our main theorem is that $\boldsymbol\Pi^1_{n+1}$determinacy for games of length $\omega^2$ implies the existence of a model of set theory with $\omega + n$ Woodin cardinals. In a first step, we show that this hypothesis implies that there is a countable set of reals $A$ such that $M_n(A)$, the canonical inner model for $n$ Woodin cardinals constructed over $A$, satisfies $A = \mathbb{R}$ and the Axiom of Determinacy. Then we argue how to obtain a model with $\omega + n$ Woodin cardinal from this.
We also show how the proof can be adapted to investigate the consistency strength of determinacy for games of length $\omega^2$ with payoff in $\Game^{\mathbb{R}} \boldsymbol\Pi^1_1$ or with $\sigma$projective payoff.
]]>We show that the Axiom of Dependent Choices, $\operatorname{DC}$, holds in countably iterable, passive premice construced over their reals which satisfy the Axiom of Determinacy, $\operatorname{AD}$, in a $\operatorname{ZF}+\operatorname{DC}_{\mathbb{R}}$ background universe. This generalizes an argument of Kechris for $L(\mathbb{R})$ using Steel’s analysis of scales in mice. In particular, we show that for any $n \leq \omega$ and any countable set of reals $A$ so that $M_n(A) \cap \mathbb{R} = A$ and $M_n(A) \vDash \operatorname{AD}$, we have that $M_n(A) \vDash \operatorname{DC}$. Furthermore, we argue that for countable premice it suffices to work in a background universe satisfying $\operatorname{ZF} + \operatorname{AC}_{\omega,\mathbb{R}}$.
]]>Of course it is more complicated than that.
Isn't it always?
, if you prefer.
Don't talk about "math accessibility" when you mean equation layout accessibility.
Mathematics is an ancient domain of human knowledge, formula or equation layout a visual layout technique developed primarily in the 19th and 20th century.
Mathematical content is far more than content that needs equation layout and equation layout appears in many more domains than just mathematics.
We will fail to make equation layout accessible if we think we can treat equation layout identically across mathematics, physics, chemistry, computer science, biology etc (and their various subfields). For example, voicing a superscript 2 as "squared" may be a reasonable heuristic for middle school mathematics but a miserable heuristic for chemistry.
We will fail to make mathematical content accessible if we only make equation layout accessible and vice versa.
Manually overriding accessible name calculations (e.g., via arialabel) on text(like) content is generally considered a last resort and it is clearly not a long term strategy for accessibility.
But we have arialabels because we know from experience that there's always a situation where you need them.
Currently, it is extremely hard to augment equation layout with arialabels let alone anything beyond simple overrides. This is a problem of authoring but much more of rendering and assistive technologies. MathMLbased solutions in browsers and AT are particularly bad at this and to some degree this cannot be fixed (we should get to that later).
Whatever solutions might arise in the future of equation layout, like everything else on the web, they must be able to work together with interspersed arialabels, together with potentially many interspersed arialabels, and ultimately with only arialabels.
In other words, deep aria labels aka aria labels all the way down must work as well.
This is a problem as ARIA has limitations when it comes to exposing custom tree structures and making them explorable.
More general authordriven augmentation must also work. Equation layout may have a natural tree structure derived from the DOM but we must be able to modify that. Ariaowns might be a solution here but right now it appears to too limited (either by spec or implementations).
If equation layout is visually inadequate, it cannot be considered accessible. The problem is: we have no solid basis for measuring this.
While TeXstyle layout is generally considered the highest quality among heavy users of equation layout, there seems to be no research evaluating this from an accessibility point of view. For example, TeX layout is largely unconcerned with K12 content and (as a print technology) has no concept for the kind of dynamic modifications we can realize on the web. While there are minor variations, e.g., elementary education preferring sansserif fonts and requiring fonts with an open glyph for 4, it's unclear to me in how far these preferences are evidencebased (pointers very welcome); in any case, they are also deeply rooted in print and might be moot on the web, e.g., there might be better ways for get whatever effect such variations are supposed to achieve.
On the web, it probably means that equation layout must be flexible enough to allow all kinds of (user or author enabled) customizations. Some obvious questions: What should happen when the lineheight changes? The letter spacing? When a transform or animation is applied to a descendant? A color changes on something with a specific color? A font (style) changes on a mathvariant? These all might be useful for accessibility purposes (e.g., with visual impairments, learning disabilities). And there are likely many more things we cannot imagine yet.
I think we greatly lack research as to what features in visual layout might be important for accessibility on the web. Without such research, we have no adequate basis on which to discuss improvements to equation layout and the standards that enable it on the web.
Heuristics are important across the assistive technology chain to recover from bad input (content). However, heuristics should not be necessary with good markup, e.g., markup that is ideal according to specs.
Equation layout is tremendously ambiguous, primarily due to its history and the limitations of print technology. For example, it is near impossible to differentiate the typical vertical fraction layout from the various other notations that share a similar vertical stack (23 children, depending on a line in between).
In other words, even high quality markup for equation layout requires heavy use of heuristics to guess the semantics.
Heuristics for nonvisual representation of equation layout have existed for a very long time (and before the web). Today, some assistive technologies integrate heuristics for equation layout when done as MathML markup.
This is a problem because most of these heuristics are fairly bad. Heuristics for equation layout are largely of low quality at scale. It is unsurprising when (e.g.) Nemeth's math speak rules were invented for a person reading to another; such limitations could easily be overcome in that situations. At the scale of the web, it is much easier to run into edge cases where heuristics are too coarse or too fine grained. An almost universal limitation is the restrictions to individual fragments of equation layout, ignoring the context (both equational and otherwise).
Relying on heuristics in AT for good content poses a serious issue (hinted to earlier): heuristics interfere with augmentation. For example, the commonly used heuristic that every superscript 2 is voiced square
, then no override may be possible; even if it is, will an override override the phrasing (e.g., to the power of two
) or also consider the superscript position? Do you need two overrides to clarify? If a heuristic identifies (1+2+3) as a summation and provides summary information (e.g. sum with three summands
), what happens when an author augment one of the + signs (say, with arialabel="times"
)? We would need to augment both the content and the heuristics. As the saying goes: and now we have two problems.
Much like with textual descriptions of other visual content (e.g., image alttext, video captions, SVG descriptions) heuristical tools (human or machine guided) should be used at authoring time.
There is a position that I encounter every once in a while: just give nonvisual users access to the visual layout and stop. That's a very appealing proposition: instead of trying to make sense of visual layout semantically, we just provide information about what letter/word is where on a twodimensional canvas. It also appeals to a basic idea of equality: visual users only have visual access, why would nonvisual users get additional information?
Unfortunately, it is a red herring: it is neither easy nor helpful nor what anyone has ever done.
It is obviously not easy on the web because layout is dynamic; if two users read a document on two different devices, they might have a very different idea as to what is where. Even within equation layout, automatic linebreaking/reflow can shift parts around, more advanced methods (e.g., MathJax's collapsing feature) can vary even more greatly.
But ignoring this larger problem, traditional equation layout has a few odd concepts that make this even more difficult. For example, movable limits can move elements from sub/superscript positions to under/overscript positions based on the context of a subexpression, without any change in the markup; reversely, this can happen when changing text content (thanks to things like the operator dictionary). Another example is the concept of embellished operators which make it difficult to identify reasonable layout blocks to describe; similarly, brackets may or may not be marked up in a way that groups open and closing brackets. Essentially, you will still need to analyze the layout semantically to identify what really belongs where and together with what because that is ultimately a question of why.
As a consequence, the idea of just describing layout is not helpful to anyone, no matter what assistive technologies they might use (even if it's just a screen). Even more so, when you have to do the same analysis as you would for identifying semantics of an expression.
What's more important is that describing layout is not what anyone has ever done (so I would surmise nobody wanted to do it). Some layout information is always ignored, other layout is always inferred as semantic. As way back as Nemeth's math speak rules for print we have had heuristics that will read any superscript 2 as squared, inferring semantics where there are none. Reversely, no assistive technology for equation layout will tell you about the dimension of a stretchy character (neither directly nor transformatively e.g. via audio cues). Again, a good example is a movable limit where rule sets get around describing (unreliable) layout in favor of heuristically determined semantics, e.g., in a sum they might voice sum from [subscript] to [superscript]
, neatly avoiding the layout. Above all, human beings do not speak equation layout as layout. Nobody says vertical bar A vertical bar
they say absolute value or determinant or something completely different, nobody says C O subscript 2
they say CO2 or carbon dioxide or possibly some more precise wording if it appears inside a checmical equation.
Of course, describing visual layout is nevertheless a decent fallback mechanism, e.g., when semantic heuristics fail but you can still recover layout information and it is important to be able to enable users to explore the layout if they need to (e.g., so as to reproduce it for their own work). But edge cases should not limit the expressiveness of accessible equation layout in general.
(An independent issue is to expose layout so that a user can guess how something was authored (e.g., when voicing gives you determinant A
, the questions may be if it was represented visually as det A
or A
.)
Accessibility is not a one way street, equation layout even more so. Accessibility must handle directionality on many axes.
Accessibility means to improve access to content no matter whether a user can access it with all theoretically possible human capacity or only using a small fragment thereof at a time. Due to its highly compressed form, equation layout requires more back and forth across a particular equation fragment as well as the entire document than most other forms of content. This is both a bug and a feature but either way it won't go away any time soon.
Accessibility means to improve interaction with content so as to allow all users to transfer knowledge better. Equation layout has a huge discrepancy between authoring formats and rendering. We must strive to improve this.
Acccessibility means improving the interaction between human beings. If two students explore a document, they should be able to do so together so that they can engage each other. Therefore, the effects of exploring content should be equivalent between different exploration methods. At the AIM workshop earlier this year, Sam Dooley told the story of a young blind person joyously celebrating that their parent could read my math
as they used an accessible authoring and rendering environment together.
Interaction in these multiple directions will provide more information to more people, enabling wider accessibility, whether people identify as AT users or not. More importantly, it will show the path towards what the web can really do for the knowledge traditionally represented in equation layout.
]]>Fraenkel's construction does not affect sets of ordinals, in particular the real numbers can still be wellordered in his models. Cohen's work, however, directly breaks that. The Dedekindfinite set added is a set of reals. In particular, the reals cannot be wellordered no more. Continue reading...
]]>Abstract: Sy Friedman introduced an inner model, which he called the \emph{stable core}, in order to study under what circumstances the universe $V$ is a class forcing extension of ${\rm HOD}$. He showed there is a definable predicate $S$, amenable to ${\rm HOD}$, such that $V$ is a class forcing extension of the structure $\langle {\rm HOD},\in,S\rangle$. Namely, there is an ${\rm ORD}$cc class partial order $\mathbb P$ definable in $\langle {\rm HOD},\in,S\rangle$ and a generic filter $G\subseteq \mathbb P$ such that ${\rm HOD}[G]=V$, however the filter $G$ itself is not definable over $V$. The predicate $S$, consisting of triples $(\alpha,\beta,n)$ for $\alpha$ and $\beta$ strong limit cardinals and $n\geq 1$ such that $H_\alpha\prec_{\Sigma_n}H_\beta$ and $\Sigma_n$collection holds in $H_\beta$, codes elementarity relations between nice enough initial segments $H_\alpha$ of $V$. Friedman's argument showed that the information necessary to define $\mathbb P$ is already contained in $S$ so that $V$ is already a class forcing extension of the stable core $\langle L[S],\in,S\rangle$.
In a joint work with Friedman and Sandra Müller, we investigated the properties of the stable core. We were interested to see whether the stable core is in any sense a canonical inner model, whether it has regularity properties, whether it is consistent with large cardinals, and whether we can code information into it using forcing. We showed that the stable core of $L[\mu]$, the canonical model for a single measurable cardinal, is $L[\mu]$ and therefore measurable cardinals are consistent with the stable core. By coding generic sets into the stable core over $L$ or $L[\mu]$, we showed that there is a generic extension of $L$ in which the ${\rm GCH}$ fails at every regular cardinal in the stable core and there is a generic extension of $L[\mu]$ in which there is a measurable cardinal which is not even weakly compact in the stable core. Our work leaves numerous open questions about the structure of the stable core in the presence of large cardinals beyond a measurable cardinal.
]]>Abstract: A set A splits an evensized set B if A contains exactly half the elements of B. For a natural number k, a splitting family on k is a collection of sets that splits any evensized subset of {1,…,k}. Variations on the concept of splitting families have appeared in applications of combinatorial search. We investigate the number of sets needed to make a splitting family on k. We give some examples and computational results, as well as theoretical partial results identifying the exact number under certain assumptions. This represents a portion of the work from the Summer 2018 REU CAD, with Bryce Frederickson, Sam Mathers, and HaoTong Yan.
]]>Victor’s work looks at the problem of taking a partial matrix (i.e. one which does not have all entries filled), and completing it to obtain a matrix with certain prescribed properties. In the course of this research, Victor used the theory of digraphs as well as a lot of linear algebra.
Ian and my involvement with Victor was facilitated by the Mentoring African Research Mathematicians programme of the London Mathematical Society; details of that scheme are here. Ian and I held a 2 year grant which allowed us to visit with, and host, Kenyan mathematicians, one of whom was Victor. The grant finished up in September 2018, although Ian and my connection with Kenya endures through supervision of two PhD students. We would like to thank the LMS for their financial support – this collaboration has been a very rewarding experience for all involved.
I should note that, in the end, Ian and I removed ourselves from the list of Victor’s official supervisors, as Moi University regulations only allowed for two supervisors on an MSc thesis. Nonetheless we are very proud to be associated with Victor’s excellent work.
]]>Abstract. We present a weak sufficient condition for the existence of Souslin trees at successor of regular cardinals. The result is optimal and simultaneously improves an old theorem of Gregory and a more recent theorem of the author.
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Abstract: John Clemens proved that the classification of countable vertextransitive graphs is Borel complete. Extending the terminology from graphs, let’s say that a structure A is vertextransitive if Aut(A) acts transitively on A. In this talk we will discuss the classification of countable vertextransitive directed graphs and linear orders. This is joint work with John Clemens and Stephanie Potter.
]]>We learn in class that a circle or sphere of radius r has curvature inversely proportional to its radius, that is it has curvature .
In this class we used baking cookies to illustrate how the curvature of an object can change over time. Seen from over top, a ball of cookie dough flattens out as it bakes.
This got me thinking about how exactly is the size of the ball of cookie dough related to the size of the cookie you get in the end? So I did some science.
A student in my class provided me with the following recipe:
Here’s a simple peanut butter recipe that’s safe for people with gluten and/or dairy allergies:
If change in curvature is desired:
 1 cup peanut butter
 3/4 – 1 cup sugar
 1 egg
 1 tsp baking soda
 tiny splash of vinegar
 tiny pinch of salt
Preheat oven to 350 degrees. Roll dough into balls and place on cookie sheet. Bake for ~1012 minutes.
For those who desire nearly constant curvature:
 1 cup peanut butter
 1 cup sugar
 1 egg
 pinch of salt
Preheat oven to 350 degrees. Roll dough into balls, place on cookie sheet and flatten to desired curvature with fork. Bake for ~1012 minutes.
After mixing everything together (using 3/4 cup sugar), since I used natural peanut butter the dough was too goopy to form into balls. So I made the following additions:
For my first batch I planned to take them out after 11 minutes, but they needed additional time, so I left them in the oven for an additional 5 minutes. This could potentially introduce some pvalue hacking because I changed my experiment in the middle of it. I don’t think the additional time changed the shape of the cookies, just how gooey they were in the inside.
I got the following results for Batch 1:
Diameter of dough ball (cm)  Diameter of cookie (cm) 
2  4.5 
2  4.5 
2.5  5 
3  6 
3  6.5 
3  6 
3.5  6.5 
3.5  7 
4  8 
3.5  8 
4  8 
4.5  9.5 
5.5  11 
The three biggest cookies pushed into each other and didn’t spread out completely. This made them a little more square than they should have been.
Batch 2 was in for a full 16 minutes, but it needed even more time! I put them in for an additional 4 minutes.
Here are those results:
Diameter of dough ball (cm)  Diameter of cookie (cm) 
5.5  11 
6.5  14.5 
The biggest cookie was pretty unstable at first, but after leaving it on the pan a little longer it firmed up.
Here’s what the cookies look like stacked from largest diameter to smallest.
Of course I had to plot this data, so I did and got the following line of best fit:
In English:
The diameter of a cookie is twice the diameter of the ball of dough used to make it.
In terms of radius, since the radius is half the diameter, and they compound, we get:
The radius of the cookie is four times the radius of the ball of dough.
Since curvature is inversely proportional to curvature, we get:
The curvature of the cookie is a quarter the curvature of the ball of dough.
I think we can actually make some interesting conclusions about this.
What size cookies should I make to avoid wasted space on my cookie sheet?
It turns out that by using this relationship between the size of the dough ball and the size of the cookie, if you have a fixed amount of dough V, and a fixed area of your cookie sheet you should make:
cookies of diameter .
I hope you had as much fun as I did! Thanks for reading.
Thanks to Robert Fajber for improvements to the graph, and Jessie Lamontagne for further directions and questions.
If you’re interested in the nittygritty details about how I came up with those formulas, here they are.
Fix . Assume we want n cookies of diameter D ( that start with diameter d). We know . We want to space out the cookies so that their bounding squares do not overlap. These squares give us
The volume of the dough gives us
This is two equations and two unknowns. Solving that gives us the desired formulas for D and n. Then we related D back to d.
]]>We prove a number of results on the determinacy of $\sigma$projective sets of reals, i.e., those belonging to the smallest pointclass containing the open sets and closed under complements, countable unions, and projections. We first prove the equivalence between $\sigma$projective determinacy and the determinacy of certain classes of games of variable length ${<}\omega^2$. We then give an elementary proof of the determinacy of $\sigma$projective sets from optimal largecardinal hypotheses. Finally, we show how to generalize the proof to obtain proofs of the determinacy of $\sigma$projective games of a given countable length and of games with payoff in the smallest $\sigma$algebra containing the projective sets, from corresponding assumptions.
]]>Sy Friedman introduced an inner model, which he called the Stable Core, in the process of trying to understand how close the inner model ${\rm HOD}$ can be to the universe $V$ [1]. An inner model is a definable (possibly with parameters) transitive submodel of the universe satisfying ${\rm ZF}({\rm C})$ and containing all the ordinals. It has long been the goal of the inner model theory program to construct a canonical inner model that is close to $V$ in the presence of very large large cardinals. Canonical inner models are built from the bottom up using absolute rules, and as a result of this construction process satisfy regularity properties, such as the ${\rm GCH}$ and $\square$, and are (generally) unaffected by enlargements of the universe via forcing. Each of these canonical inner models, for example, $L$, $K^{DJ}$, $L[U]$, are close to the universe $V$ in the absence of certain large cardinals, but are very far from a universe having those large cardinals. There are several ways in which we can request that an inner model is close to $V$. The inner model can have some form of covering, agree on large cardinals, or reach the universe $V$ by forcing, so that $V$ is a forcing extension of it.
The canonical inner models ultimately attempt to generalize Gödel's constructible universe $L$, making it compatible with large cardinals. Another inner model introduced by Gödel, the collection ${\rm HOD}$ of all hereditarily ordinal definable sets, lacks the fine structure of the canonical inner models and therefore their absoluteness and regularity properties, but it makes up for it by being compatible with all known large cardinals and in fact all known set theoretic assertions. This is essentially because using coding any set or class can become ordinal definable in a forcing extension. Every set $A$ is coded by a set of ordinals because we can recover a set from its transitive closure, the transitive closure can be coded by a binary relation on some cardinal, which maps to it via the Mostowski collapse, and a set of pairs of ordinals can in turn be coded by a subset of the cardinal. Now given a subset $A$ of a cardinal $\kappa$, we use forcing to code it into the continuum pattern of the extension, thus making $A$ ordinal definable in the extension. Indeed, in this manner, we can code the entire universe $V$ into the continuum function of a class forcing extension, making $V$ be precisely the ${\rm HOD}$ of this extension $V[G]$ (this was apparently first shown by Roguski [2], the coding idea is due to McAloon). It follows that any universe is the ${\rm HOD}$ of some larger universe, so that ${\rm HOD}$ can satisfy any (believed to be) consistent settheoretic assertion. It is known that ${\rm HOD}$ can be quite far from $V$. Cheng, Hamkins, and Friedman showed that it is consistent that every measurable cardinal is not even weakly compact in ${\rm HOD}$ and that there can be a supercompact cardinal that is not even weakly compact in ${\rm HOD}$ [3]. Cummings, Friedman, and Golshani showed that it is also consistent that $(\alpha^+)^{\rm{HOD}}<\alpha^+$ for every infinite cardinal $\alpha$ (missing reference). Woodin, however has conjectured that in the presence of very large large cardinals ${\rm HOD}$ will be much closer to $V$.
In further trying to understand the relationship between ${\rm HOD}$ and $V$, Sy Friedman defined the ordinal definable stability predicate $S$ and showed that $V$ is a forcing extension of the structure $({\rm HOD},S)$, ${\rm HOD}$ together with a predicate for $S$ [1]. The stability predicate $S$ codes the elementarity relations between initial segments $H_\alpha$ of $V$. It consists of triples $(\alpha,\beta,n)$ where $\alpha$ and $\beta$ are strong limit cardinals such that $H_\alpha$ and $H_\beta$ satisfy $\Sigma_n$Collection and $H_\alpha\prec_{\Sigma_n}H_\beta$. More precisely, Friedman showed that in the structure $({\rm HOD}, S)$, there is a definable class partial order $\mathbb P$ for which there is a generic filter $G\subseteq \mathbb P$ such that ${\rm HOD}[G]=V$. The result is quite subtle in that even though $(V,G)\models{\rm ZFC}$, $G$ is not definable over $V$. Hamkins and Reitz later showed that it is consistent for $V$ to not be a class forcing extension of ${\rm HOD}$, so some additional information is indeed required to make $V$ a forcing extension of ${\rm HOD}$ [4].
Friedman's result showed that $V$ is already a class forcing extension of the structure $(L[S],S)$, which is the Stable Core of the title of the post. Because $S$ is ordinal definable, $L[S]\subseteq {\rm HOD}$, and Friedman showed that consistently $L[S]$ can be smaller than ${\rm HOD}$. It remained unknown whether the new inner model had any regularity properties or whether it was consistent with large cardinals. In a joint work with Sy Friedman and Sandra Müller we establish some further properties that are consistent with the Stable Core [5].
We generalized the recent work of Kennedy, Magidor, and Väänänen on the model $L[{\rm Card}]$ [6] to show that $K^{DJ}$ and $L[U]$ are always contained in the Stable Core. Recall that $K^{DJ}$ is the DoddJensen core model below a measurable cardinal and $L[U]$ is the canonical inner model for one measurable cardinal. This shows, in particular, that the Stable Core of $L[U]$ is $L[U]$, so that the Stable Core can have a measurable cardinal. Same techniques, using Kunen's generalization of the $L[U]$ construction, can be used to show that the Stable Core can have a number of measurable cardinals. The next open question is whether the Stable Core can have a measurable limit of measurable cardinals. The question arises because Kennedy, Magidor, Väänänen and Welch (the result is still unpublished) showed that if the universe has a (little more than) a measurable limit of measurable cardinals, then $L[{\rm Card}]$ is a very simple model, in particular, it satisfies the ${\rm GCH}$ and has no measurable cardinals.
It is relatively easy to code information into the Stable Core over canonical models ($L$, $K^{DJ}$, or $L[U]$) because we can use their definability inside the Stable Core to compare the changes we made to the elementarity relations between the $H_\alpha$ to the original relations. Using a coding along these lines, we show that any set which can be added generically to $L$ (or $L[U]$) can be coded into the Stable Core of a further forcing extension. From this it follows that the ${\rm GCH}$ can fail at every regular cardinal in the Stable Core, that ${\rm CH}$ can fail and Martin's Axiom can hold in the Stable Core, that any cardinal of $L$ can become countable in the Stable Core, etc. We also show that there is a forcing extension of $L[U]$ in which the measurable cardinal $\kappa$ remains measurable but $\kappa$ is not even weakly compact in the Stable Core. Thus, measurable cardinals are not downward absolute to the Stable Core. Because we don't know how to code information into the Stable Core over arbitrary models, these results leave open the general question about what does the Stable Core look like the presence of larger large cardinals such as a measurable limit of measurable cardinals.
The open questions here are numerous! Here are a few. It is easy to see using coding that the ${\rm HOD}$ of ${\rm HOD}$ can be smaller than ${\rm HOD}$. Can the Stable Core of the Stable Core be smaller? Is there a bound on the large cardinals compatible with the Stable Core? Or are larger large cardinals downward absolute to the Stable Core? Is the Stable Core of $M_1$, the canonical model for one Woodin cardinal, $M_1$?
So often times, it seems, it is very tempting to talk about theorems that you haven't finished writing their proofs in full. Usaully, we put "work in progress" to indicate that this is something not fully verified, not fully vetted (at the very least by ourselves). Continue reading...
]]>Large Cardinals in the Stable Core
Abstract: The Stable Core $\mathbb{S}$, introduced by Sy Friedman in 2012, is a proper class model of the form $(L[S],S)$ for a simply definable predicate $S$. He showed that $V$ is generic over the Stable Core (for $\mathbb{S}$definable dense classes) and that the Stable Core can be properly contained in HOD. These remarkable results motivate the study of the Stable Core itself. In the light of other canonical inner models the questions whether the Stable Core satisfies GCH or whether large cardinals is $V$ imply their existence in the Stable Core naturally arise. We answer these questions and show that GCH can fail at all regular cardinals in the Stable Core. Moreover, we show that measurable cardinals in general need not be downward absolute to the Stable Core, but in the special case where $V = L[\mu]$ is the canonical inner model for one measurable cardinal, the Stable Core is in fact equal to $L[\mu]$.
This is joint work with Sy Friedman and Victoria Gitman.
Slides for this talk are available on request.
]]>How to obtain Woodin cardinals from the determinacy of long games
Abstract: We will study infinite two player games and the large cardinal strength corresponding to their determinacy. For games of length $\omega$ this is well understood and there is a tight connection between the determinacy of projective games and the existence of canonical inner models with Woodin cardinals. For games of arbitrary countable length, Itay Neeman proved the determinacy of analytic games of length $\omega \cdot \theta$ for countable $\theta > \omega$ from a sharp for $\theta$ Woodin cardinals. We aim for a converse at successor ordinals and sketch how to obtain $\omega+n$ Woodin cardinals from the determinacy of $\boldsymbol\Pi^1_{n+1}$ games of length $\omega^2$. Moreover, we outline how to generalize this to construct a model with $\omega+\omega$ Woodin cardinals from the determinacy games of length $\omega^2$ with $\Game^{\mathbb{R}}\boldsymbol\Pi^1_1$ payoff.
This is joint work with Juan P. Aguilera.
]]>Catalog description: An introduction to the language and methods of reasoning used throughout mathematics. Topics include propositional and predicate logic, elementary set theory, proof techniques including mathematical induction,functions and relations, combinatorial enumeration, permutations and symmetry.
]]>Catalog description: Lebesgue measure on the reals, construction of the Lebesgue integral and its basic properties. Advanced linear algebra and matrix analysis. Fourier analysis, introduction to functional analysis.
]]>Abstract: A major segment of modern research in set theory focuses on the topics of forcing and large cardinals. Forcing, introduced by Cohen to show the independence of the Continuum Hypothesis, is a technique for building settheoretic universes satisfying a desired list of properties. Large cardinal axioms are strong axioms positing the existence of very large infinite objects and (often) elementary embeddings between settheoretic structures. These axioms form a hierarchy against which the strength of any settheoretic assertion can be measured. Forcing and large cardinals interact in a number of unexpected ways. In this talk, I will discuss a relatively new avenue of research involving the notion of virtual large cardinals. Given a large cardinal property $A$ characterized by the existence of elementary embeddings of firstorder structures, we say that the property $A$ holds virtually if embeddings on structures from the universe $V$ characterizing $A$ exists in forcing extensions of $V$. Virtual large cardinals are much weaker than their original counterparts, for instance being compatible with the constructible universe $L$. This line of research leads naturally to considering a virtual version of Vopěnka's Principle, a large cardinal principle which has found applications in other branches of math. Virtual Vopěnka's Principle states that given a proper class of firstorder structures in a common language, two of them must elementary embed in a forcing extension of $V$. I will discuss the consistency strength of the new principle, which like other virtual large cardinal principles, is compatible with $L$, and some open questions concerning stronger version of the principle, where we demand that the forcing extension in which the embeddings exist preserves a large initial segment of the universe. Parts of this work are joint with Bagaria, Schindler, and Hamkins.
I gave a 4lecture tutorial at the 11th Young Set Theory Workshop, Lausanne, June 2018.
Title: In praise of Csequences.
Abstract. Ulam and Solovay showed that any stationary set may be split into two. Is it also the case that any fat set may be split into two? Shelah and BenDavid proved that, assuming GCH, if the successor of a singular cardinal carries a special Aronszajn tree, then it also carries a distributive Aronszajn tree. What happens if we relax “special Aronszajn” to just “Aronszajn”? Shelah proved that the product of two $\omega_2$cc posets need not be $\omega_2$cc. How about the product of countably many $\omega_2$Knaster posets?
It turns out that a common strategy for answering all of the above questions is the study of Csequences. In this series of lectures, we shall provide a toolbox for constructing Csequences, and unveil a spectrum of applications.
Downloads:
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This is an indepth description of the basic combinatorial and geometric techniques in graph theory. It is a very thorough and helpful document with many Olympiad level problems for each topic. (No solutions are given.)
Topics include:
A large collection of problems and topics almost all of which have solutions or hints.
Topics include:
Contains a concise list of important results together with a guided discussion to five example problems that use graph theory.
An introduction to the probabilistic method in graph theory along with 10 problems.
A list of about 30 problems and solutions in graph theory.
Topics:
This is a 4 page article that introduces Ramsey Theory for graphs and arithmetic progressions and its historical relation to the IMO.
A collection of 12 topics about coloring graphs and planes. There are many problems with solutions.
This series of slides states 7 results in extremal combinatorics that are really the same.
Topics:
Well, obviously, if choice failed then the answer is no, just by taking \(x=x\). But what if we remove that option. Namely, if the inner model is not the entire universe, then choice holds. Continue reading...
]]>Abstract: Lebesgue introduced a notion of density point of a set of reals and proved that any Borel set of reals has the density property, i.e. it is equal to the set of its density points up to a null set. We introduce alternative definitions of density points in Cantor space (or Baire space) which coincide with the usual definition of density points for the uniform measure on ${}^{\omega}2$ up to a set of measure $0$, and which depend only on the ideal of measure $0$ sets but not on the measure itself. This allows us to define the density property for the ideals associated to tree forcings analogous to the Lebesgue density theorem for the uniform measure on ${}^{\omega}2$. The main results show that among the ideals associated to wellknown tree forcings, the density property holds for all such ccc forcings and fails for the remaining forcings. In fact we introduce the notion of being stemlinked and show that every stemlinked tree forcing has the density property.
This is joint work with Philipp Schlicht, David Schrittesser and Thilo Weinert.
Slides are available here.
]]>Long games and Woodin cardinals
Abstract: Itay Neeman proved the determinacy of analytic games of length $\omega \cdot \theta$ for countable $\theta > \omega$ from a sharp for $\theta$ Woodin cardinals. We aim for a converse at successor ordinals and show how to obtain $\omega+1$ Woodin cardinals from the determinacy of analytic games of length $\omega \cdot (\omega+1)$.
This is joint work with Juan P. Aguilera.
Notes for this talk are available here.
]]>All spaces are assumed to be separable and metrizable. We show that, assuming the Axiom of Determinacy, every zerodimensional homogeneous space is strongly homogeneous (that is, all its nonempty clopen subspaces are homeomorphic), with the trivial exception of locally compact spaces. In fact, we obtain a more general result on the uniqueness of zerodimensional homogeneous spaces which generate a given Wadge class. This extends work of van Engelen (who obtained the corresponding results for Borel spaces) and complements a result of van Douwen.
]]>My regular meetings with Sam are one of my great pleasures. Since our friendship is almost exclusively virtual, it's surprising that we have kept it alive for quite a while now. Almost weekly, we get on video to work on new ideas or and projects  or just chitchat about life, work and being young parents (or parents of young kids anyway).
Perhaps unsurprisingly given that we met at a Young Set Theory Workshop, it all started with us setting up Set Theory Talks which grew turned into settheory.mathtalks.org (and you can get a subdomain with the same semiautomatic features if you like). Nowadays, Assaf is handling the real work of grooming the site while Sam and I continue the little bits of technical support as needed. Later, I pulled Sam into maintaining mathblogging.org with me after Fred and Felix dropped out.
I suppose it was inevitable ever since I left research 6 years ago. But, really, life just got busier and hosting more complex so late last year, Sam and I decided that we do not have the time (nor the abilities) to continue hosting more and more sites. We let everyone know what's happening and helped them in their transitions.
Yesterday, we pulled the plug on all the WordPress goodness we had built over the years. And thus, Booles' Rings has passed  in its original form, a literal network of WordPress sites for academics.
Of course, none of the sites have disappeared. In many ways we're now where I wanted to get everyone to: not just researchers taking the web seriously as a fixed point of a research career, building a stable presence of one's research persona, overcoming the cacophony of everchanging, deadordying department pages where Google page rank inevitably yields the outdated ones.
No, I always wanted more: get researchers to take this platform seriously, embrace it as a medium with new (and old) idiosyncrasies. Take it seriously as a tool that you should wield confidently and, in need, wield independently, no matter what. No more lock in.
And this is where Booles' Rings is now. The people are still here, the site now merely works as lightweight connection (and an aggregator). And no matter how we all approach this medium, it's fine. Whether it's selfhosted WordPress installations or statically generated sites, whether slowchurning long form or neardaily activity, whether researchonly or life's breadth. The point is not that one thing is better than the other. The point is that we are on the web, our shared and world wide web  and that we're here to stay.
Even though I left research years ago, I still love to follow this community. I look forward to the next 7 years of Booles' Rings.
]]>This morning I came back to something I had drafted after Joanmarie Diggs proposed a session on a particular hack (but the group didn't end up focusing on this in the unconferencestyle workshop setting).
One of my goto examples when explaining that Presentation MathML is devoid of semantics is the <mfrac>
element. While it clearly hints at being a fraction, the spec itself clearly states that it is not, semantically, a fraction but that it may be used for completely different things that visually look like fractions, e.g., binomial coefficients or the Legendre symbol; in fact, you can find many even less fractionlike examples (such as logical deductions) in the wild because a vertical stack with a properly aligned line is simply a neat layout feature.
Since Presentation MathML never specifies semantics, let's look how Content MathML encodes fractions. The spec would have you write something like <cn type="rational">22<sep/>7</cn>
. It's a terribly good example for how Content MathML is a bit too strong in its abstraction for human communication (also, check the transcription to Presentation MathML). As an aside, if you need more examples of why <mfrac>
is not meaningful, just search that section.
Anyway, at the workshop Joanie had proposed the following. It turns out, Firefox is too lazy ahem too performanceoriented to sanitize invalid ARIA roles. This allows you to experiment with madeup properties fairly easily (assuming you can modify your screenreader of choice).
So for example, you could slap an ariamath
attribute to your markup and this would show up in OSlevel accessibility inspectors such as aViewer or accerciser. What Joanie had in mind (I believe) is that we could have tried to expose additional information this way so that Joanie could hack something into ORCA and then get Mick and Reef to modify NVDA or David to modify ChromeVox (and maybe even hear what Glen thinks of it from a JAWS perspective). And yes, all these incredible people were actually there in person.
Since an idea that I had proposed to the group (exploring web components for mathematical documents) also didn't stick, I thought I'd combine the two when I get the chance. Luckily, I had a long flight home.
Et voilà, a custom element fraction that adds ariamath
roles to itself magically (using fraction
, numerator
, denominator
andfractionline
).
See the Pen AIM Workshop custom element: fraction by Peter Krautzberger (@pkra) on CodePen.
It's not much and not really a "document"level element as I was thinking about (then again, Joanie had hoped for improving an <mfrac>
directly) but it's a nice (nonfunctional) concept, and perhaps helpful when thinking about ARIA roledescription
.
There are two standard approaches to carrying out the forcing construction over a model of ${\rm ZFC}$ set theory: with partial orders or with complete Boolean algebras. The two approaches yield the same forcing extensions because every partial order densely embeds into a complete Boolean algebra, and when a partial order densely embeds into another partial order, the two have the same forcing extensions. Although the partial order construction can be viewed as more straightforward, the complete Boolean algebras approach offers some advantages. For instance, there are theorems about forcing which have no known proofs without the use of Boolean algebras. One such fundamental result is the Intermediate Model Theorem, which states that if a universe $V\models{\rm ZFC}$ and $W\models{\rm ZFC}$ is an intermediate model between $V$ and one of its setforcing extensions, then $W$ is itself a forcing extension of $V$. The theorem makes a fundamental use of the Axiom of Choice, but a weaker version of it still holds for models of ${\rm ZF}$. If $V\models{\rm ZF}$ and $V[a]\models{\rm ZF}$, with $a\subseteq V$, is an intermediate model between $V$ and one of its setforcing extensions, then $V[a]$ is itself a setforcing extension of $V$. Grigorieff in [1] attributes the Intermediate Model Theorem to Solovay.
The standard Boolean algebras approach is not available in the context of class forcing because most class partial orders cannot be densely embedded into a sufficiently complete class Boolean algebra. Set forcing uses complete Boolean algebras, those which have suprema for all their subsets, because completeness is required for assigning Boolean values to formulas in the forcing language. With a class Boolean algebra, which has suprema for all its subsets, we can still define the Boolean values of atomic formulas, but the definition of Boolean values for existential formulas needs to take suprema of subclasses, meaning that we must require a Boolean algebra to have those in order to be able to construct the Booleanvalued model. However, as shown in [2], a class Boolean algebra with a proper class antichain can never have this level of completeness. Thus, only ${\rm ORD}$cc Boolean algebras (having setsized antichains) can potentially have suprema for all their subclasses. Indeed, it is shown in [2] that every ${\rm ORD}$cc partial order densely embeds into a complete Boolean algebra.
In this article we nevertheless show that the Boolean algebras approach to class forcing can be carried out in sufficiently strong secondorder set theories, for example, the theory KelleyMorse plus the Choice Scheme, using hyperclass Boolean completions. We apply the Boolean algebras approach to show that the ${\rm ZF}$analogue of the Intermediate Model Theorem holds for models of KelleyMorse plus the Choice Scheme.
Let us call an extension $\mathscr W$ of a model $\mathscr V$ of secondorder set theory simple if it is generated by the classes of $\mathscr V$ together with a single new class. In particular, every forcing extension of $\mathscr V$ is simple. We show that every simple intermediate model between a model of ${\rm KM}+{\rm CC}$ and one of its class forcing extensions is itself a forcing extension, so that the Intermediate Model Theorem holds for simple extensions. We also show that an intermediate model between a model of ${\rm KM}+{\rm CC}$ and one of its class forcing extensions need not be simple, and thus the Intermediate Model Theorem can fail. For models of ${\rm KM}$, the Intermediate Model Theorem can fail even where the forcing has the ${\rm ORD}$cc because a model of ${\rm KM}$ and its forcing extension by ${\rm ORD}$cc forcing can have nonsimple intermediate models. We don't know whether this can happen for models of ${\rm KM}+{\rm CC}$. Finally, we show that if an intermediate model $\mathscr W$ between a model $\mathscr V\models{\rm KM}+{\rm CC}$ and its forcing extension $\mathscr V[G]$ has a definable global wellordering of classes, and we have additionally that $\mathscr W$ is definable in $\mathscr [G]$, then $\mathscr W$ must be a simple extension of $\mathscr V$.
Abstract: We explore spherical geometry and trigonometry. This poster consists of four parts: (1) Using classical trigonometry to figure out how large is the Earth and the distance to the Moon; (2) How to find the distance between two places in the Earth; (3) Napier’s Rule I and II and an application on the sea with a rightangle triangle; (4) Delambre’s first analogy and an example of an oblique triangle.
]]>On the other hand, I find the act of reading the scholarship of math education to be dreadful and unpleasant. It is filled with jargon and heroworship.
That being said, I’ve been extremely lucky to have great mentors and colleagues to bounce ideas off of. I’ve collected some of this advice in a Reddit post, which I’ll recreate here.
Here is some vocabulary that is commonly used when discussing math pedagogy, or pedagogy in general. In general the literature is pretty annoying and frustrating; there’s lots of jargon and lots of stuff is toohigh level.
So, this one has been on the back burner for a while. And it actually started as two separate projects that merged and separated and merged again. Continue reading...
]]>There are two standard ways to do forcing: using partial orders or using complete Boolean algebras. Since every partial order densely embeds into a complete Boolean algebra and whenever two partial orders densely embed, they produce the same forcing extensions, the two approaches to forcing are essentially interchangeable. But meanwhile each approach offers distinct advantages.
The kind of new object we would like to have in the forcing extension dictates what the conditions in the partial order should be. If you would like to add a new real, make the partial order consist of finite binary sequences. If you would like to add a tree, make the partial order consist of small trees. It is usually clear how different conditions in the partial order alter the properties of the new object. The Boolean completion of the partial order breaks the direct connection between the properties of the object we would like to add and the conditions in the forcing, which is precisely why pretty much no one uses the Boolean algebras approach in forcing practice. The Boolean algebras approach however offers both philosophical and practical advantages.
We often speak of the forcing relation for a partial order being definable. But what does the forcing relation really mean when we are talking about forcing over the entire universe $V$ and not just some toy countable model? In this context it does not make sense to say that $p\Vdash\varphi$ means that whenever $p$ is an element of a generic filter $G$, then $V[G]\models\varphi$. On the other hand, the Booleanvalued model construction with a complete Boolean algebra makes sense without reference to any transitive set models. Indeed, using any ultrafilter $U$ on the Boolean algebra, we can turn the Booleanvalued model into a definable model $M\models{\rm ZFC}$ of the form $\bar V[G]$, a forcing extension of submodel $\bar V$, where $V$ elementarily embeds into $\bar V$. So that by passing from $V$ to $\bar V$, a model with the same theory, we get access to both the universe and its forcing extension.
There are theorems about forcing which have no known proofs without the use of complete Boolean algebras. A fundamental result about forcing is the Intermediate Model Theorem, which states that every intermediate universe $W\models{\rm ZFC}$ between a universe $V$ and its forcing extension $V[G]$ is itself a forcing extension of $V$. Indeed, if $V[G]$ is a forcing extension by $\mathbb P$ and $\mathbb B_{\mathbb P}$ is a Boolean completion of $\mathbb P$, then $\mathbb B_{\mathbb P}$ has a complete subalgebra $\mathbb D$ such that $W=V[\mathbb D\cap G]$ is a forcing extension by $\mathbb D$. Grigorief in [1] attributes the Intermediate Model Theorem to Solovay. The theorem makes a fundamental use of the Axiom of Choice, but is true in a weaker form for models of ${\rm ZF}$. If $V[a]\models{\rm ZF}$ with $a\subseteq V$ is an intermediate universe between $V\models{\rm ZF}$ and its forcing extension $V[G]$, then $V[a]$ is a forcing extension of $V$.
Everything that has been said so far holds true for set partial orders. What about class partial orders? Analyzing the properties of class partial orders is best done in a secondorder setting where we have objects for classes as well as sets. One of the weakest secondorder theories is the GödelBernays set theory ${\rm GBC}$, so let's take it for the moment as our secondorder foundation. We will think of models of secondorder set theory as triples $\mathscr V=\langle V,\in,\mathcal C\rangle$, where $V$ is the collection of sets and $\mathcal C$ is the collection of classes. If $\mathbb P\in\mathcal C$ is partial order and $G\subseteq \mathbb P$ is $\mathscr V$generic, then the forcing extension $\mathscr V[G]=\langle V[G],\in,\mathcal C[G]\rangle$, where $V[G]$ is all interpretations of $\mathbb P$names and $\mathcal C[G]$ is all interpretations of class $\mathbb P$names, which are collections of pairs $\langle \sigma,p\rangle$ where $\sigma$ is a $\mathbb P$name and $p\in\mathbb P$. Now we can talk about the properties of class partial orders.
From the perspective of forcing, class partial orders don't behave anywhere as nicely as set partial orders. Class partial orders may not preserve ${\rm GBC}$. Think for example, of the partial order to add bijection from $\omega$ onto ${\rm ORD}$. The forcing relation for a class partial order may not be definable because it can, for instance, code in a truth predicate for $\mathscr V$. Two class partial orders can densely embed but produce different forcing extensions. Class partial orders may not have Boolean completions. (The results are from [2]) To understand this last point, let's be more precise about the kind of Boolean completion we would like a class partial order to have.
The completeness of a Boolean algebra is used in defining the Boolean values of formulas in the forcing language. Suppose $\mathbb B$ is a Boolean algebra. For example, the Boolean value of an atomic assertion $$[[\sigma\in \tau]]=\bigwedge_{\langle \mu,b\rangle\in \tau}[[\sigma=\mu]]\cdot b$$ and the Boolean value of an existential assertion $$[[\exists x\varphi(x,\tau)]]=\bigvee_{\sigma\in V^{\mathbb B}}[[\varphi(\sigma,\tau)]].$$ So if $\mathbb B$ is class, then the definition of Boolean values for atomic assertions requires the existence suprema for sets (setcompleteness), but the existential assertions require the existence of suprema for classes as well (classcompleteness).
A class partial order can be densely embedded into a setcomplete Boolean algebra if and only if its forcing relation is definable [3]. So in ${\rm GBC}$, it is not the case that every class partial order can be embedded into a setcomplete Boolean algebra. To define the forcing relation however requires only a bit more comprehension, already in ${\rm GBC}$ together with $\Pi^1_1$comprehension (for assertions with a single class quantifier) every class partial order has a definable forcing relation (indeed this is already true for a much weaker theory ${\rm GBC}+{\rm ETR}_{\rm {ORD}}$, see [4]). So in the much stronger theory KelleyMorse ${\rm KM}$ (which consists of ${\rm GBC}$ together with comprehension for all secondorder assertions) every class partial order can be embedded into a setcomplete Boolean algebra. But indeed, it will never be possible to embed every class partial order into a classcomplete Boolean algebra. A Boolean algebra with a proper class antichain can never be class complete, and therefore no class partial order with a proper class antichain can be embedded into such a Boolean algebra [3]. But without class completeness, we cannot define the Booleanvalued model!
What happens when we try to carry out the standard Boolean completion construction with a class partial order? The elements of the completion are subsets of $\mathbb P$ that are regular cuts (a cut is subset of $\mathbb P$ that is closed downwards and a cut $U$ is regular if whenever $p\notin U$, then there is $q\leq p$ such that $U_q\cap U=\emptyset$, where $U_q$ is the cut consisting of all conditions in the cone below $p$). If $\mathbb P$ is a class, then regular cuts are definable subclasses of $\mathbb P$, and so the collection of regular cuts of $\mathbb P$ is a hyperclass  a (secondorder) definable collection of classes. What properties does this hyperclass, call it $\mathbb B_{\mathbb P}$, have? We can definably impose a Boolean operations structure on it in the usual way, so it is a Boolean algebra. How complete is it? First, let's explain how some hyperclasses can actually be quite small, namely classsized. We will say that a hyperclass, given a formula $\varphi(X,A)$, is coded by a class $S$ if the classes satisfying $\varphi(X,A)$ are precisely the slices of $S$, where a class $T$ is a slice of $S$ if there is a set $a$ such that $T=\{y\mid \langle y,a\rangle\in S\}$. We should think of coded hyperclasses as being classsized. The hyperclass Boolean algebra $\mathbb B_{\mathbb P}$ is classcomplete in the sense that it is complete for all coded hyperclasses. Given a hyperclass coded by $S$, its join is the least regular cut containing the union of all slices $S_a$. But because the elements of $\mathbb B_{\mathbb P}$ are now classes, it should be intuitively clear that to have any hope of using it to define a Booleanvalued model, we need $\mathbb B_{\mathbb P}$ to be complete for all hyperclasses, not just the coded ones. Remarkably it turns out that given any partial order $\mathbb P$ with a proper class antichain, if $\mathbb B_{\mathbb P}$ is hyperclass complete, then we have comprehension for all secondorder assertions, and therefore ${\rm KM}$ holds [5]. Thus, the completeness of the hyperclass object is directly connected to the amount of comprehension a model satisfies.
In models of ${\rm KM}$, the hyperclass object $\mathbb B_{\mathbb P}$ has all the desired properties. It is complete for all hyperclasses and indeed, as aught to be the case because it has a classsized dense subpartialorder, all its hyperclass antichains are coded. But it is still very difficult if not impossible to define the Booleanvalued model with a Boolean algebra whose elements are classes. A natural solution to this problem is to move a slightly stronger secondorder set theory KelleyMorse together with the Choice Scheme.
The Choice Scheme ${\rm CC}$ is a choice principle (or a collection principle depending on the point of view) for classes which states for every secondorder assertion $\varphi(x,X,A)$ that if for every set $x$, there is a witnessing class $X$ such that $\varphi(x,X,A)$ holds, then there is a single class $Y$ collecting witnesses for every set $x$, in the sense that $\varphi(x,Y_x,A)$ holds for every set $x$ (where $Y_x$ is the $x$th slice of $Y$ defined as above). KelleyMorse does not prove even the weakest instances of the Choice Scheme, those for firstorder assertions and making just $\omega$many choices [6]. But nevertheless the two theories ${\rm KM}$ and ${\rm KM}+{\rm CC}$ are equiconsistent, basically because the "constructible universe" of a model of ${\rm KM}$ satisfies ${\rm KM}+{\rm CC}$. The theory ${\rm KM}+{\rm CC}$ has one remarkable feature. It is biinterpretable with a very wellunderstood firstorder set theory. Given a model $\mathscr V\models{\rm KM}+{\rm CC}$ we can consider its class wellfounded relations. For instance, $\mathscr V$ has relations coding ${\rm ORD}+{\rm ORD}$, ${\rm ORD}\times\omega$, $V\cup{\{V\}}$, etc. We can view such relations as coding transitive sets that sit "above" the sets of $V$. Modulo isomorphism, we can define a membership relation on the equivalence classes of these relations resulting in a firstorder structure extending $V$. We will call this structure the companion model $M_{\mathscr V}$ of $\mathscr V$. The model $M_{\mathscr V}$ satisfies the theory ${\rm ZFC}^_I$, consisting of the axioms of ${\rm ZFC}$ without powerset $()$, with the assertion that there is a largest cardinal $\kappa$ which is inaccessible ($I$). Natural models of ${\rm ZFC}^_I$ are $H_{\kappa^+}$ for an inaccessible cardinal $\kappa$. The $V_\kappa$ of $M_{\mathscr V}$ consists of the sets $V$ of $\mathscr V$ and the subsets of $V_\kappa$ are the classes of $\mathscr V$. In the other direction if $M\models{\rm ZFC}^_I$, then $\mathscr V=\langle V_\kappa^M,\in,\mathcal C\rangle$, where $\mathcal C$ consists of the subsets of $V_\kappa$ in $M$, is a model of ${\rm KM}+{\rm CC}$ whose companion model $M_{\mathscr V}$ is isomorphic to $M$.
Thus, whenever we work in a model $\mathscr V\models{\rm KM}+{\rm CC}$, we might as well be working in its companion model $M_{\mathscr V}$. But now the trick is that in $M_{\mathscr V}$, the class partial order $\mathbb P$ is a set (subset of $V_\kappa^{M_{\mathscr V}}$) and the hyperclass $\mathbb B_{\mathbb P}$ is a classcomplete Boolean algebra with setsized antichains. In $M_{\mathscr V}$, it is now easy to define the collection $M_{\mathscr V}^{\mathbb B_{\mathbb P}}$ of $\mathbb B_{\mathbb P}$names as well the Boolean values of all assertions in the forcing language, using the completeness of $\mathbb B_{\mathbb P}$. In this sense, we have the Boolean algebras approach to forcing in models of ${\rm KM}+{\rm CC}$.
One consequence of this is that we get the ${\rm ZF}$analogue of the Intermediate Model Theorem for models of ${\rm KM}+{\rm CC}$. Let us say that $\mathscr W$ is a simple extension of $\mathscr V\models{\rm KM}+{\rm CC}$ if $\mathscr W$ is generated by the classes of $\mathscr V$ together with a single class. In particular, forcing extensions of $\mathscr V$ are simple. Using, the Booleanvalued model, we can show that every intermediate simple extension $\mathscr W\models{\rm KM}+{\rm CC}$ between a model $\mathscr V\models{\rm KM}+{\rm CC}$ and its forcing extension $\mathscr V[G]\models{\rm KM}+{\rm CC}$ is itself a forcing extension of $\mathscr V$. The result is optimal because it is possible to have intermediate models between a model $\mathscr V\models{\rm KM}+{\rm CC}$ and its forcing extension $\mathscr V[G]\models\rm KM+{\rm CC}$ that are not simple, and therefore cannot be forcing extensions themselves. [5]
This is joint work with Carolin Antos and SyDavid Friedman.
Joint work with Chris LambieHanson.
Abstract. The productivity of the $\kappa$chain condition, where $\kappa$ is a regular, uncountable cardinal, has been the focus of a great deal of settheoretic research.
In the 1970s, consistent examples of $\kappa$cc posets whose squares are not $\kappa$cc were constructed by Laver, Galvin, Roitman and Fleissner. Later, ZFC examples were constructed by Todorcevic, Shelah, and others. The most difficult case, that in which $\kappa = \aleph_2$, was resolved by Shelah in 1997.
In this work, we obtain analogous results regarding the infinite productivity of strong chain conditions, such as the Knaster property. Among other results, for any successor cardinal $\kappa$, we produce a ZFC example of a poset with precaliber $\kappa$ whose $\omega^{\mathrm{th}}$ power is not $\kappa$cc.
To do so, we carry out a systematic study of colorings satisfying a strong unboundedness condition. We prove a number of results indicating circumstances under which such colorings exist, in particular focusing on cases in which these colorings are moreover closed.
Downloads:
So I recently wrote about a fragment of mathematical content and a big part of it was the problem of stretchy braces. After building the "plain" HTML+CSS example at the end (reusing an extremely clever solution from the upcoming MathJax v3), I kept thinking: this should be easier. Luckily, this year I'm dedicating a chunk of my spare time to the MathOnWeb Community Group's new task force focused on CSS, looking for (old and new) ideas that might help simplify equation layout using CSS.
So one thing led to another and I found myself coming back to an old thought of mine.
Stretchy characters like those braces, what are they really? Like, really really?
Let's look at what they are called. As a matter of fact, they are called various things but the most generic term is possibly bracket. However in the context of equation layout, the more common terminology might be delimiter and fence. In particular, MathML provides an <mfenced>
tag (though for various reasons the equivalent <mrow>
+<mo>
constructions tend to be preferred by most tools).
Now both brackets, fences and delimiters sound awfully similar to a very common concept. Where do you usually put up a fence? Where do you delimit something? At a border. It's a small idea, obviously, but what if we could solve the problem of stretchy constructions using borders?
What if somebody else already has?
Well, you could go visit codepen and simply search for brace and, lo and behold, you find 4 perfectly fine specimens in CSS. Turns out, designers love pretty things, who'd have thunk.
If you dig a little deeper, you'll end up with basically three approaches.
The first one (with several interesting forks) is by Lauren Herda.
See the Pen SingleElement Curly Brace by Lauren Herda (@lrenhrda) on CodePen.
It is really pretty  look Ma, a single div! (Except that it doesn't quite work on Chrome since an <hr>
gets overflow:hidden
from the user agent style sheet.)
That was fun. Let's do two more: one from Jakob Christoffersen
See the Pen curly braces css by Jakob Christoffersen (@MasterThrasher) on CodePen.
and one from @mexn:
See the Pen CSS Curly Brace by Markus (@mexn) on CodePen.
Both are slighly more complicated than the first one. Instead of the radial gradient for the middle piece, they both use 6 elements with borderradius (though the last one has only two elements with pseudoelements). If you dive into their forks, you'll find lots of interesting variations, too.
The point is: this problem has in a very real sense actually been solved in CSS and you can do lots of fun variations yourself.
Such as this one
See the Pen stretchy brace by Peter Krautzberger (@pkra) on CodePen.
or this one
See the Pen stretchy brace, singlediv by Peter Krautzberger (@pkra) on CodePen.
(Fun fact: using percentages in the border radius leads to some really cute behavior across sizes.)
Now you might say it hasn't solved the real problem. Here are a couple of counterarguments:
It has no character! Gasp! It's true that in typical print equation layout engines you'll still have a character there. Well, you could just add a hidden one, no?
It doesn't work well on small sizes! In typical print equation layout, you'll see several sizes of a brace being used for smaller heights (with possibly slight design variations for readability) after which the layout would switch over to a stretchy constructions (made up of several glyphs stitched together). This is a very interesting problem to solve. And you know what? This touches on one of the hottest topics of CSS discussions in the past few years: it is a perfect use case for container queries. Go add a use case and push the web forward for everyone!
But perhaps current CSS is sufficient and someone will find a clever approach to achieve a similar effect. As I mentioned above, percentages in border radius have a neat effect; there is a lot of room to play with once you stop thinking about everything in terms of print traditions.
It's not semantic! Gosh. What exactly does a (stretched) brace represent, semantically speaking? And, should you have decided to imbue it with such rich meaning yourself, are you really unable to expose the relevant information using the web platform's rich accessibility stack? No? Excellent  you should file a bug with ARIA and help push the web forward for everyone!
It can't look like font x! Some fonts have a really tricky curly brace with basically an S shape in each half. I admit my CSSfoo is not good enough to do that. But besides the fact that a better designer might find a solution, I find the tradeoff acceptable. And if there's a limitation in CSS, please file a bug with the CSS WG and help push the web forward for everyone!
It can't do delimiter y! There are quite a few brackets, some more complex than others (Mathematical left white tortoise shell bracket anyone?) but few of those are used in stretchy ways and fewer still occur often (for comparison, the STIX2 fonts support ~30 delimiters). I really don't have a problem with such edge cases remaining difficult for the time being if we can solve a practical problem for 99% of use cases. And if you do, ... you know what to do.
So let's do two more, the most important ones:
Parentheses,
See the Pen Stretchy parenthesis by Peter Krautzberger (@pkra) on CodePen.
and square brackets
See the Pen Stretchy brackets by Peter Krautzberger (@pkra) on CodePen.
See now, that wasn't so hard?
I suspect that if we work a bit harder to unstuck ourselves from the traditions of (print) equation layout engines, then we might just find a lot of interesting solutions like this; solutions that help make equation layout on the web as easy as as designing a good page layout with CSS; solutions that work with the grain of the web; solutions that perhaps even lack but help identify (and resolve) shortcomings in the web platform that affect a much wider community; solutions that help move the web forward.
PS: I've started a little collection on codepen. Ping me if you see something that might fit!
]]>Abstract: We show that for any countable homogeneous ordered graph $G$, the conjugacy problem for automorphisms of $G$ is Borel complete. In fact we establish that each such $G$ satisfies a strong extension property called ABAP, which implies that the isomorphism relation on substructures of $G$ is Borel reducible to the conjugacy relation on automorphisms of $G$.
]]>But I want my own problems page, and it's my site. So to celebreate the new website, I created just that. For the first couple of problems, I've chosen to focus on the axiom of choice. And I don't think that I have much choice, but to keep that interest running. But I can promise that this is not the only type of problems that I will add there. Continue reading...
]]>The dissertation studies the ordinary (complex) character theory of M_{11} and M_{12}; it includes the foundations of character theory, as well as details on how to construct M_{11} and M_{12} via the notion of “transitive extension”. I think Sam has done a beautiful job and should be congratulated!
We are in the process of writing up a paper including some of Sam’s results. In fact the paper comes from a slightly different point of view. Our main result is the following:
Theorem
The point of this theorem is that we are able to construct the character table of G using only the assumption about multipletransitivity – there is no direct reference to the Mathieu groups in this paper.
In the course of this research, I asked a question on MathOverflow here. Now seems a good time to thank the contributors to that discussion, especially Frieder Ladisch, for their help!
]]>It is a static website, because I am tired of the WordPress format for a long long time now. So for the occasion, I also got a new domain, karagila.org. Isn't this nice? The only domain and all the links should work, at least for the foreseeable future. So there's nothing to worry about linkrot for now. But please do update your links! Continue reading...
]]>This is part of a series of posts aimed at helping my mom, who is not a scientist, understand what I’m up to as a mathematician.
Lately, Artificial Intelligence (AI) has made some remarkable milestones. There are computers that are better than humans at the strategy board game GO and at Poker. Computers can turn pictures into short moving clips and can “enhance” blurry pictures as in television crime shows. They can also produce new music in the style of Bach or customized to your tastes. It’s all very exciting, and it feels pretty surreal; remember back when Skype video calling felt like the future?
I’m going to give you a broad overview for how these types of AI work, and how they learn. There won’t be any equations or algebra.
Before we jump into the computer stuff, let’s make our very first AI. Well, this will be more “I” than “AI”, because I want you to play a game. You are going to be the “AI” that’s going to learn a task!
I want you to play Zrist for about 5 minutes (or longer if you like it). It’s a fun little platform game. See how far you can get. My best score was 37 400. We’ll use this experience to help describe how AI works. Okay, go play now!
Welcome back! I hope you had fun playing that game.
I want you to think about these questions, and give an answer to each of them. (It’s not a test, there are no wrong answers.)
We’ll come back to your answers in a moment. For now, I want you to watch a bit of a video of an AI (called Mar I/O) learning to play the original 1985 Super Mario Brothers. Watch maybe the first 4 or 5 minutes, and then skip to the middle of the video. You only need to watch a little bit to get the sense of what’s going on.
(If you like this, you can watch a livestream of Mar I/O’s attempts to beat the game level by level.)
First of all, this program starts off only knowing a couple of things:
Here are some things it doesn’t know:
If you’re interested, Mar I/O is a Recurrent Neural Net. There are other types of AI, but this is the we’ll look at today.
So at first it tries random stuff to increase its fitness score: jumping, standing still, ducking, running left, and none of these seem to increase its fitness. Then, when it presses right, mario starts progressing in the level and its fitness score goes up.
This is called training the AI. It measures its progress against a fitness score, and it reinforces behaviour that increases that score. i.e. It starts to favour pressing right because that seems to increase its fitness score.
This works great until it gets to the first enemy and mario runs right into it and dies. After a couple more tries, it starts to experiment some more (just like it was trying random things at the beginning of the level). Around the 2:20 mark of the video, Mar I/O presses the jump button right before the enemy and successfully clears it, allowing mario to move further right and increase its fitness score.
To recap:
Let’s go back to the platform game you played and look at how you learned to play the game.
What was the goal of the game?
How did you know you were doing well at the game?
I asked you to get as far in the level as you could; that was your goal. The game kept track of it by telling you your current high score. That was your fitness score!
How did you adapt to the rules changes? Did you get them on the first try?
If you’re anything like me, when the rules changed for the first time you thought, “Oh crap, what’s this?”, and then promptly died when the screen said “Mode: lag”. What were you supposed to do?! No one told you what to do!
When my character turned invisible, the screen stopped scrolling and I wasn’t sure what to do. At that point I just pressed buttons until it started to scroll again; i.e. I tried random things when I got stuck. As I continued to get stuck and unstuck, I recognized that I was getting stuck at the short walls, and that jumping over them saved me then. Trying the same trick saved me again when I was invisible. i.e. I was training on the short walls.
This is very similar to how Mar I/O trains and learns.
For comparison, here’s a video of one of the best Mario players in the world, CarlSagan42, taking 18 hours to beat an extremely difficult fanmade level. (Warning: there are a bunch of swear words.)
Notice a couple things:
These are all in common with Mar I/O.
How did you make decisions about what to do next? (What did you look for, and what did you ignore?)
In Zrist, you were probably looking for gaps (to jump over), those horrible red death blocks, and big walls to slide under. For each of these you developed a reaction: “When I see a gap, then I press C (to jump over it)”.
For each of these you had to remember a task: If I see a gap, then I jump over it.
For AI like Mar I/O, it stores these tasks by associating visual cues and inputs with button presses. For example, when it sees a wide open space it learns to press the right button. When it sees a gap in the ground it learns to press the A button (to jump).
Now Mar I/O doesn’t have any extra code which tells it “this is what a pit looks like” or “this is what a pipe is” or anything like that, (although it can see enemies as black tiles, it doesn’t know what an enemy is).
Each time it succeeds at increasing its fitness score it strengthens the connections between the visual cues and the sequence of button presses that got it there. Each connection like this is stored in the AI as an “artificial neuron”. So when you were playing Zrist, you probably developed a neuron relating to gaps (“If gap, then jump”), one for tall walls (“If tall wall, then slide”), and many others.
The very cool thing about modern AI is that you typically don’t need to tell it what or how many artificial neurons to make ahead of time, Mar I/O adds neurons as it learns. It’s just like how you didn’t need to know how many types of obstacles you would face in Zrist, you built up a list as you went. This is very powerful!
The flip side to this is that after Mar I/O learns to beat a level, we humans will have a hard time understanding what it’s using to make its decisions. It won’t always be clear to us what visual elements (called “features”) it’s using to make its decisions.
Hopefully you see some of the parallels between the way AIs learn things and the way humans learn things. There are a lot of similarities. Mimicking human learning has been very useful for creating AIs.
I’m going to point out a couple other ways that humans learn that help illustrate ways in which AI can learn.
Have you ever driven somewhere familiar and then forgotten how you got there? You were on autopilot. Similarly, have you ever been doing something with your hands, like playing the piano, but when you stop to think about what you’re actually doing, the task suddenly becomes much harder. This sort of muscle memory is very similar to what Mar I/O is doing. It learns sequences of moves and button presses, but there is no underlying reasoning.
I skipped over a big part of Mar I/O’s learning, which is that it actually contains many different “styles” of players (called species); it’s not just a single mario learning. After each species completes about 10 attempts at beating the level, we rank the species by which achieved the highest fitness. We then delete the bottom 10% of the species and replace them by blending some of the best species (in a process called breeding). This ensures that if one of the mediocre species discovers something useful (like shooting fireballs can kill enemies) it still has a chance to give that idea to the best performers. Similarly, the best performers get to share their ideas with the mediocre performers.
One of these processes is called a generation. For easy levels, Mar I/O only needed 40 or so generations. For difficult levels, Mar I/O needed over 250 generations! It can take a long time for these random mutations to produce helpful effects.
If this feels a lot like evolution, well that’s because it is! These AI learn by evolving and refining their strategies. This is a very deep and powerful idea, but I’ve already gone on long enough, so I’ll save it for another time.
The advancement of AI evokes many feelings: Awe and wonder, but also fear and skepticism. So I’ll end this post talking about what the future might look like.
AI are machines. The term artificial intelligence might better be described as artificial skill. Mar I/O is only able to maximize a fitness score. It’s quite good at that, but that’s the only thing it can do. This AI is highly specialized to Super Mario Brothers. While it’s possible that the underlying Mar I/O code can be adapted to other games (like Mario Kart), it requires human knowledge, judgement and skill to adapt it to other settings.
We don’t expect that Mar I/O will turn ever turn into a killer robot. At its core, Mar I/O is a (complicated) machine that presses buttons and is good at increasing a number (its fitness score).
If you want to learn more about AI, here are some good resources based on your background.
I just want nice pictures and videos. NO MATH!:
I am comfortable with the topics described here, but want a bit more substance:
I have a degree in math or computer science and want all the details. Leave no stone unturned:
Large cardinals from the determinacy of games
Abstract: We will study infinite two player games and the large cardinal strength corresponding to their determinacy. In particular, we will consider mice, which are sufficiently iterable models of set theory, and outline how they play an important role in measuring the exact strength of determinacy hypotheses. After summarizing the situation within the projective hierarchy for games of length $\omega$, we will go beyond that and consider the determinacy of even longer games. In particular, we will sketch the argument that determinacy of analytic games of length $\omega \cdot (\omega+1)$ implies the consistency of $\omega+1$ Woodin cardinals. This part is joint work with Juan P. Aguilera.
]]>Models of arithmetic are twosorted structures, having two types of objects, which we think of as numbers and sets of numbers. Their properties are formalized using a twosorted logic with separate variables and quantifiers for numbers and sets. By convention, we will denote number variables by lowercase letters and sets variables by uppercase letters. The language of secondorder arithmetic is the language of firstorder arithmetic $\mathcal L_A=\{+,\cdot,<,0,1\}$ together with a membership relation $\in$ between numbers and sets. A multitude of secondorder arithmetic theories, as well as the relationships between them, have been extensively studied (see [1]).
An example of a weak secondorder arithmetic theory is ${\rm ACA_0}$, whose axioms consist of the modified Peano axioms, where instead of the induction scheme we have the single secondorder induction axiom $$\forall X [(0\in X\wedge \forall n(n\in X\rightarrow n+1\in X))\rightarrow \forall n (n\in X)],$$ and the comprehension scheme for firstorder formulas. The latter is a scheme of assertions stating for every firstorder formula, possibly with class parameters, that there is a set whose elements are exactly the numbers satisfying the formula. One of the strongest secondorder arithmetic theories is ${\rm Z}_2$, often referred to as full secondorder arithmetic, which strengthens comprehension for firstorder formulas in ${\rm ACA}_0$ to full comprehension for all secondorder assertions. This means that for a formula with any number of secondorder quantifiers, there is a set whose elements are exactly the numbers satisfying the formula. The reals of any model of ${\rm ZF}$ is a model of ${\rm Z}_2$. We can further strengthen the theory ${\rm Z}_2$ by adding choice principles for sets: the choice scheme and the dependent choice scheme.
The choice scheme is a scheme of assertions, which states for every secondorder formula $\varphi(n,X,A)$ with a set parameter $A$ that if for every number $n$, there is a set $X$ witnessing $\varphi(n,X,A)$, then there is a single set $Y$ collecting witnesses for every $n$, in the sense that $\varphi(n,Y_n,A)$ holds, where $Y_n=\{m\mid \langle n,m\rangle\in Y\}$ and $\langle n,m\rangle$ is any standard coding of pairs. More precisely, an instance of the choice scheme for the formula $\varphi(n,X,A)$ is $$\forall n\exists X\varphi(n,X,A)\rightarrow \exists Y\forall n\varphi(n,Y_n,A).$$ We will denote by $\Sigma^1_n$${\rm AC}$ the fragment of the choice scheme for $\Sigma^1_n$assertions, making an analogous definition for $\Pi^1_n$, and we will denote the full choice scheme by $\Sigma^1_\infty$${\rm AC}$. The reals of any model of ${\rm ZF}+{\rm AC}_\omega$ (countable choice) satisfy ${\rm Z}_2+\Sigma^1_\infty$${\rm AC}$. It is a folklore result, going back possibly to Mostowski, that the theory ${\rm Z}_2+\Sigma^1_\infty$${\rm AC}$ is biinterpretable with the theory ${\rm ZFC}^$ (${\rm ZFC}$ without the powerset axiom, with Collection instead of Replacement) together with the statement that every set is countable.
The dependent choice scheme is a scheme of assertions, which states for every secondorder formula $\varphi(X,Y,A)$ with set parameter $A$ that if for every set $X$, there is a set $Y$ witnessing $\varphi(X,Y,A)$, then there is a single set $Z$ making infinitely many dependent choices according to $\varphi$. More precisely, an instance of the dependent choice scheme for the formula $\varphi(X,Y,A)$ is $$\forall X\exists Y\varphi(X,Y,A)\rightarrow \exists Z\forall n\varphi(Z_n,Z_{n+1},A).$$ We will denote by $\Sigma^1_n$${\rm DC}$ the dependent choice scheme for $\Sigma^1_n$assertions, with an analogous definition for $\Pi^1_n$, and we will denote the full dependent choice scheme by $\Sigma^1_\infty$${\rm DC}$. The reals of a model of ${\rm ZF}+{\rm DC}$ (dependent choice) satisfy ${\rm Z}_2+\Sigma^1_\infty$${\rm DC}$.
It is not difficult to see that the theory ${\rm Z}_2$ implies $\Sigma^1_2$${\rm AC}$, the choice scheme for $\Sigma^1_2$assertions. Models of ${\rm Z}_2$ can build their own version of Gödel's constructible universe $L$. If a model of ${\rm Z}_2$ believes that a set $\Gamma$ is a wellorder, then it has a set coding a settheoretic structure constructed like $L$ along the wellorder $\Gamma$. It turns out that models of ${\rm Z}_2$ satisfy a version of Shoenfield's absoluteness with respect to their constructible universes. For every $\Sigma^1_2$assertion $\varphi$, a model of ${\rm Z}_2$ satisfies $\varphi$ if and only its constructible universe satisfies $\varphi$ with set quantifiers naturally interpreted as ranging over the reals. All of the above generalizes to constructible universes $L[A]$ relativized to a set parameter $A$. Thus, given a $\Sigma^1_2$assertion $\varphi(n,X,A)$ for which the model satisfies $\forall n\exists X\varphi(n,X,A)$, the model can go to its constructible universe $L[A]$ to pick the least witness $X$ for $\varphi(n,X,A)$ for every $n$, because $L[A]$ agrees when $\varphi$ is satisfied, and then put the witnesses together into a single set using comprehension. So long as the unique witnessing set can be obtained for each $n$, comprehension suffices to obtain a single set of witnesses. How much more of the choice scheme follows from ${\rm Z}_2$? The reals of the classical FefermanLévy model of ${\rm ZF}$ (see [2], Theorem 8), in which $\aleph_1$ is a countable union of countable sets, is a $\beta$model of ${\rm Z}_2$ in which $\Pi^1_2$${\rm AC}$ fails. This is a particulary strong failure of the choice scheme because, as we explain below, $\beta$models are meant to strongly resemble the full standard model $P(\omega)$.
There are two ways in which a model of secondorder arithmetic can resemble the full standard model $P(\omega)$. A model of secondorder arithmetic is called an $\omega$model if its firstorder part is $\omega$, and it follows that its secondorder part is some subset of $P(\omega)$. But even an $\omega$model can poorly resemble $P(\omega)$ because it may be wrong about wellfoundedness by missing $\omega$sequences. An $\omega$model of secondorder arithmetic which is correct about wellfoundedness is called a $\beta$model. The reals of any transitive ${\rm ZF}$model is a $\beta$model of ${\rm Z}_2$. One advantage to having a $\beta$model of ${\rm Z}_2$ is that the constructible universe it builds internally is isomorphic to an initial segment $L_\alpha$ of the actual constructible universe $L$.
The theory ${\rm Z}_2$ also implies $\Sigma^1_2$${\rm DC}$ (see [1], Theorem VII.9.2), the dependent choice scheme for $\Sigma^1_2$assertions. In this article, we construct a symmetric submodel of a forcing extension of $L$ whose reals form a model of secondorder arithmetic in which ${\rm Z}_2$ together with $\Sigma^1_\infty$${\rm AC}$ holds, but $\Pi^1_2$${\rm DC}$ fails. The forcing notion we use is a tree iteration of a forcing for adding a real due to Jensen.
Jensen's forcing, which we will call here $\mathbb P^J$, introduced by Jensen in [3], is a subposet of Sacks forcing constructed in $L$ using the $\diamondsuit$ principle. The poset $\mathbb P^J$ has the ccc and adds a unique generic real over $L$. The collection of all $L$generic reals for $\mathbb P^J$ in any model is $\Pi^1_2$definable. Jensen used his forcing to show that it is consistent with ${\rm ZFC}$ that there is a $\Sigma^1_3$definable nonconstructible real [3]. Recently Lyubetsky and Kanovei extended the "uniqueness of generic filters" property of Jensen's forcing to finitesupport products of $\mathbb P^J$ [4]. They showed that in a forcing extension $L[G]$ by the $\omega$length finite supportproduct of $\mathbb P^J$, the only $L$generic reals for $\mathbb P^J$ are the slices of the generic filter $G$. The result easily extends to $\omega_1$length finite supportproducts as well.
We in turn extend the ``uniqueness of generic filters" property to tree iterations of Jensen's forcing. We first define finite iterations $\mathbb P^J_n$ of Jensen's forcing $\mathbb P^J$, and then define an iteration of $\mathbb P^J$ along a tree $\mathcal T$ to be a forcing whose conditions are functions from a finite subtree of $\mathcal T$ into $\bigcup_{n<\omega}\mathbb P_n^J$ such that nodes on level $n$ get mapped to elements of the $n$length iteration $\mathbb P_n^J$ and conditions on higher nodes extend conditions on lower nodes. The functions are ordered by extension of domain and strengthening on each coordinate. We show that in a forcing extension $L[G]$ by the tree iteration of $\mathbb P^J$ along the tree ${}^{\lt\omega}\omega_1$ (or the tree ${}^{\lt\omega}\omega$) the only $L$generic filters for $\mathbb P_n^J$ are the restrictions of $G$ to level $n$ nodes of tree. We proceed to construct a symmetric submodel of $L[G]$ which has the tree of $\mathbb P_n^J$generic filters added by $G$ but no branch through it. The symmetric model we construct satisfies ${\rm AC}_\omega$ and the tree of $\mathbb P_n^J$generic filters is $\Pi^1_2$definable in it. The reals of this model thus provide the desired $\beta$model of ${\rm Z}_2$ in which $\Sigma^1_\infty$${\rm AC}$ holds, but $\Pi^1_2$${\rm DC}$ fails.
Our results also answer a longstanding open question of Zarach from [5] about whether the Reflection Principle holds in models of ${\rm ZFC}^$. The Reflection Principle states that every formula can be reflected to a transitive set, and holds in ${\rm ZFC}$ by the LévyMontague reflection because every formula is reflected by some $V_\alpha$. In the absence of the von Neumann hierarchy, it is not clear how to realize reflection, and indeed we show that it fails in $H_{\omega_1}\models{\rm ZFC}^$ of the symmetric model we construct.
Abstract: Lebesgue introduced a notion of density point of a set of reals and proved that any Borel set of reals has the density property, i.e. it is equal to the set of its density points up to a null set. We introduce alternative definitions of density points in Cantor space (or Baire space) which coincide with the usual definition of density points for the uniform measure on ${}^{\omega}2$ up to a set of measure $0$, and which depend only on the ideal of measure $0$ sets but not on the measure itself. This allows us to define the density property for the ideals associated to tree forcings analogous to the Lebesgue density theorem for the uniform measure on ${}^{\omega}2$. The main results show that among the ideals associated to wellknown tree forcings, the density property holds for all such ccc forcings and fails for the remaining forcings. In fact we introduce the notion of being stemlinked and show that every stemlinked tree forcing has the density property.
This is joint work with Philipp Schlicht, David Schrittesser and Thilo Weinert.
Slides are available on request.
]]>Well. Actually no. When I was a dewy eyed freshman, I had taken all my classes with 300 students from computer science and software engineering (BenGurion University has changed that since then). Our discrete mathematics professor was someone who was renowned as somewhat careless when it comes to details in questions and stuff like this (my older brother took calculus with the same professor about ten years before, one day he didn't show up to class, when my brother and two others went to see if he is at his office, he was surprised to find out that today is Tuesday). Continue reading...
]]>In the mean time, here’s a nice graph. It answers a question posed on Reddit that uses Chromatic numbers to solve a real life problem!
Here’s another irrelevant picture.
]]>Abstract: A linear order is called scattered if the rational order doesn’t embed into it. Scattered linear orders admit a derivative operation and an ordinal rank. In this talk we introduce some machinery needed to study the complexity of the classification of scattered linear orders of a given countable rank.
]]>It's also difficult because most people in this field like this confusion, especially if they have a stake in it. It's obviously a better sales pitch to say you're helping all of STEM even if you're actually working on a set of (arguably tricky) visual/print layout techniques. I don't want to sound too cynical here; for many people it does come from the heart, they think they are helping STEM this way and it is what drives them. Besides, as they say, you cannot change others only yourself.
These days I spent much more time on the document level and, mostly, on mathematical documents. That brings up a slew of interesting problems but many are too ephemeral to share. The other day I had a particularly interesting piece of content as it highlights some aspects of the problem of this identification.
In this paper you find the following
The layout captured in this image combines a label (5.4) with an ordered list of three mathematical statement, one of which include a sublist of two items. Of course, these statements include quite a few bits of equational content but those aren't that important here. Instead, what's interesting is that a stretchy brace is used a visual cue that connects the single label with the list of statements, aligning its center with the label and extending to the height of the list.
How do you realize this kind of layout on the web? (And, for that matter, in LaTeX?) Before answering that, it's worth to dive a little deeper.
There are two conflicting details here. On the one hand, the label (as per source and context) is actually an equation label. This means the authors intended this list of statements (each being a selfcontained sentence with several equational elements interspersed) to be treated as a single piece of equational content. Much like tables, images, or (since we're in a math paper) theorem environments, this is an important piece of structural information and should not be lost.
On the other hand, the list is (nested) ordered (text) list and it is encoded as such by the authors. This is obviously an important piece of structural information and should not be lost.
And that's a bit of a problem both for the web and for LaTeX: there's no system for equation layout with a concept for ordered list builtin. And there's no text layout system with stretchy braces.
If you look in the TeX source of the paper, you'll see how this was hacked using \parbox
. On the web, you have a harder time since in practical terms you can't really do this kind of hack of switching from equation layout to text layout. In theory (i.e., HTML5 spec dream land), you could try something like this
<math side="left">
<mtable>
<mlabeledtr>
<mtd>
<mtext>(5.4)</mtext>
</mtd>
<mtd>
<mo>{</mo>
<mtext>
<ol>
...
</ol>
</mtext>
</mtd>
</mlabeledtr>
</mtable>
</math>
Now this won't work that well in real life. But the real question for me is: is that even correct? (in which sense)? This is a <math>
element consisting really only of text while the purely visual brace is the only element with "semantic" markup. Hm...
I find this one interesting because the problem is a case of visual layout clouding one's judgement. You want to use stretchy braces, so in TeX you need math mode and the rest follows pretty "rationally", no matter the hackiness. After all, it's print; no need to care about anything but the looks.
On the one hand, there's the gut reaction to say that authors should not do things like this. This may be based on the simple principle that, when you need to hack around a lot, you're probably doing something wrong.
A less toxic response may be to criticize the content structure: should this really be an equation label? Isn't it more like a theoremenvironment anyway? If not, should this enumeration not be numbered as subequations? And isn't the brace a legacy from organizing content on a blackboard rather than something for print layout to mimic (let alone web layout)?
If I was one of the authors, I'd probably respond grumpily: how dare you question that this is the best (perhaps not good but best) way to represent this particular piece of mathematical content that I arrived at after years of study of a deep and complex research topic?
And they'd be right because this really only evades the two actual problems: the confusion of "equation" and "mathematical fragment" and the problem of stretchy characters.
On the one hand, it's clear that this is a (complicated) unit of mathematical information. It must be treated as one. And while I would argue it is not an equation/formula (and certainly not in the sense of "equational layout" let alone MathML's idea of it), if the authors want to count it as such, there should be a way. But on the web we're severely limited when it comes to marking anything "an equation", especially when it structures like regular lists come into play.
From a layout perspective is, however, the only notable problem is the stretched brace. It has no meaning here (if it ever has); it's merely a stylistic element to help visually connect a list with a label. It is not "mathematics" or even "equational" in any sense of the word. And yet with the current state of web technology, the only way to realize it is by using tools specialized for precisely equation layout (and usually with misleading "semantics" to boot).
But we should be able to do this, no?
Here's an example (using a technique of pure CSS stretchy braces developed by Davide Cervone for MathJax v3).
See the Pen case study: arxiv.org/1412.8106 by Peter Krautzberger (@pkra) on CodePen.
I read up on the changes in the HTML 5.3 working draft and realized that my HTML5ish example above (using an ordered list inside MathML) is not even valid HTML  oh my! As it turns out, the integration of MathML into HTML states that only phrasing content is allowed inside MathML token elements (and lists are not phrasing content). Well, one more reason never to use MathML on the web  but you already knew that.
]]>]]>Pass on what you have learned. Strength, mastery. But weakness, folly, failure also. Yes, failure most of all. The greatest teacher, failure is.
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Abstract: Questions about infinity are fascinating, and can lead into deep mathematical topics in set theory. The mathematics of infinite sets wasn’t clearly understood until Cantor defined cardinal numbers in the late 19th century, stating that two sets are the same size if there is a onetoone correspondence between them. One surprising result from set theory, first proved by Cantor in 1873, is that there are precisely as many rational numbers (fractions) as there are counting numbers. Over one hundred years later, mathematicians Neil Calkin and Herbert S. Wilf published a more elegant proof of this fact.
This article is the result of our work to develop the ideas in the CalkinWilf proof, so that they would be accessible to the teachers in our three different Math Teachers’ Circles. We designed an investigation into the hyperbinary numbers (itself a 19th century topic that predates Cantor’s work on cardinality) and developed the Tree of Fractions, much in the style of Calkin and Wilf. We asked teachers to make observations, ask questions, and convince each other of the veracity of their claims.
]]>First off, there's Equations ≠ Math (Or: Equation layout as a print artifact) (archive.org). This somewhat of a continuation (and hopefully a refinement) on #196.
You should also totally register for my upcoming workshop on equation rendering in ebooks at Ebookcraft in March!
]]>I've never been one for looking back at the end of a year. But since the last year was complex (and this one is set up to be equally so) I thought maybe I should motivate myself by looking ahead to the things I want to write about this year (including things in my actual schedule for 2018).
Ok, maybe stop here; it's a lot already.
]]>Suppose that f is a transcendental entire function. In 2014, Rippon and Stallard showed that the union of the escaping set with infinity is always connected. In this paper we consider the related question of whether the union with infinity of the bounded orbit set, or the bungee set, can also be connected. We give sufficient conditions for these sets to be connected, and an example a transcendental entire function for which all three sets are simultaneously connected. This function lies, in fact, in the Speiser class.
It is known that for many transcendental entire functions the escaping set has a topological structure known as a spider’s web. We use our results to give a large class of functions in the EremenkoLyubich class for which the escaping set is not a spider’s web. Finally we give a novel topological criterion for certain sets to be a spider’s web.
]]>
The FatouJulia iteration theory of rational and transcendental entire functions has recently been extended to quasiregular maps in more than two real dimensions. Our goal in this paper is similar; we extend the iteration theory of analytic selfmaps of the punctured plane to quasiregular selfmaps of punctured space.
We define the Julia set as the set of points for which the complement of the forward orbit of any neighbourhood of the point is a finite set. We show that the Julia set is nonempty, and shares many properties with the classical Julia set of an analytic function. These properties are stronger than those known to hold for the Julia set of a general quasiregular map of space.
We define the quasiFatou set as the complement of the Julia set, and generalise a result of Baker concerning the topological properties of the components of this set. A key tool in the proof of these results is a version of the fast escaping set. We generalise various results of MartiPete concerning this set, for example showing that the Julia set is equal to the boundary of the fast escaping set.
]]>
Abstract: In this talk I presented the notation and machinery of forcing, the statement of Martin’s axiom, and some wellknown applications in the area of Baire category and measure theory.
]]>The restriction to the study of only the definable large collections of sets is a limitation of firstorder set theory which prevents us from exploring some natural properties of settheoretic universes. For instance, consider the long standing open question whether Reinhardt cardinals are consistent with ${\rm ZF}$, which has been revisited only a few days ago in this article. The Reinhardt cardinal is the critical point of an elementary embedding $j:V\to V$. It is not difficult to show that there cannot be a definable elementary $j:V\to V$ in a model of ${\rm ZF}$, so the open question is about the existence of an undefinable such embedding. Other recent examples of the use of general classes comes from the study of inner model reflection principles. Motivated by a question of Neil Barton, Barton, Caicedo, Fuchs, Hamkins, and Reitz recently introduced and studied the Inner Model Reflection Principle stating that every firstorder formula reflects to a proper inner model [1]. The statement of the principle cannot be expressed in firstorder set theory because it requires quantifying over classes. Along similar lines, Friedman had previously introduced the Inner Model Hypothesis which states that if a firstorder sentence holds in an outer model (extension universe) of an inner model, then it already holds in some inner model [2]. For a long time it was not clear in what framework this principle could be formalized because it requires not only quantifying over classes but also referring to classes that are potentially outside the universe itself.
So how do we undertake a general study of classes? What is the framework in which we can have undefinable classes and where we can study the properties of classes in the same way we study sets? This framework is secondorder set theory, formalized in a twosorted logic with separate objects and quantifiers for sets and classes. Models of secondorder set theory are triples $\mathscr V=\langle V,\in,\mathcal C\rangle$ where $\mathcal C$ is the collection of classes of $\mathscr V$. One of the weakest reasonable axiomatizations of secondorder theory is the GödelBernays set theory ${\rm GBC}$ whose axioms consist of the ${\rm ZFC}$ axioms for sets, extensionality, replacement, and existence of global wellorder axioms for classes, together with a weak comprehension scheme stating that every firstorder formula defines a class. If a universe of set theory has a definable global wellorder, then it together with its definable classes is a model of ${\rm GBC}$. Indeed, ${\rm GBC}$ is equiconsistent with ${\rm ZFC}$ and has the same firstorder consequences as ${\rm ZFC}$. If we just add to ${\rm GBC}$ comprehension for $\Sigma^1_1$formulas (formulas with a single class existential quantifier), we get a much stronger theory with many desirable properties. The theory ${\rm GBC}$ + $\Sigma^1_1$Comprehension implies that that any two metaordinals (class wellorders) are comparable, that we can iterate the $L$ construction along any metaordinal, that there is an iterated truth predicate along any metaordinal, that determinacy holds for open class games, and that the class forcing theorem holds.
A truth predicate is a class of Gödel codes of firstorder formulas obeying Tarskian truth conditions. Tarski's Theorem on the undefinablity of truth implies that a truth predicate cannot be definable and therefore ${\rm GBC}$, because it can have models with only the definable classes, cannot imply the existence of such a class. Indeed, the existence of a truth predicate class implies $\text{Con}({\rm ZFC})$, $\text{Con}(\text{Con}({\rm ZFC}))$ and much more. ${\rm GBC}$ + $\Sigma^1_1$Comprehension implies that there is a truth predicate for every structure $\langle V,\in, A\rangle$ for a class $A$. In particular, if $T_0$ is the truth predicate (for $\langle V,\in,A\rangle$), then we have a truth predicate $T_1$ for the structure $\langle V,\in, T_0,A\rangle$, that is we have truth for truth. How far can we iterate the truth operation? ${\rm GBC}$ + $\Sigma^1_1$Comprehension implies that we get an iterated truth predicate along any metaordinal.
By analogy with games on $X^\omega$, for a set $X$, where the players take turns playing elements from $X$ for $\omega$many steps, in the secondorder context we can consider games on ${\rm ORD}^\omega$. It turns out ${\rm GBC}$ + $\Sigma^1_1$Comprehension implies determinacy for all such open class games [3].
The strength of the forcing construction comes from the Forcing Theorem which states that the forcing relation (for a fixed firstorder formula) is definable. The analogue of the Forcing Theorem for class partial orders says that the forcing relation (for a fixed firstorder formula) is a class. The Class Forcing Theorem can fail in a model of ${\rm GBC}$ because there are class forcing notions from whose forcing relation for atomic formulas we can define a truth predicate. But ${\rm GBC}$ + $\Sigma^1_1$Comprehension implies the Class Forcing Theorem.
Surprisingly, in ${\rm GBC}$ + $\Sigma^1_1$Comprehension, we can even formalize Friedman's Inner Model Hypothesis because the properties of outer models can be expressed via a strong logic, called $V$logic, whose proof system is expressible in this theory [4].
Indeed, it turns out that most of these principles are implied by a weaker natural theory ${\rm GBC}$ + ${\rm ETR}$ elementary transfinite recursion. The principle ${\rm ETR}$, which is an analogue of the Recursion Theorem in firstorder set theory, states that every firstorder definable recursion along a metaordinal has a solution. The principle ${\rm ETR}$ implies over ${\rm GBC}$ that we can iterate the $L$ construction along any metaordinal. Over ${\rm GBC}$, the principle ${\rm ETR}$ is equivalent to determinacy for clopen class games and to the existence of an iterated truth predicate along any metaordinal [3]. The Class Forcing Theorem is equivalent over ${\rm GBC}$, to the principle $\rm {ETR}_{\rm {ORD}}$, stating that we can perform recursions along ${\rm ORD}$ [5]. The amount of available ${\rm ETR}$ gives a natural hierarchy of secondorder set theories above ${\rm GBC}$ with ${\rm ETR}_\omega$ already implying the existence of a truth predicate.
The only principle we have considered so far which is known to be stronger than ${\rm ETR}$ is open determinacy, a result due to Sato [6]. Hamkins and Woodin showed recently that open determinacy implies that forcing does not add metaordinals, a natural analogue to the statement that forcing does not add ordinals (personal communication).
Of course, the amount of available comprehension itself gives a hierarchy of secondorder set theories culminating with the KelleyMorse set theory ${\rm KM}$, which consists of ${\rm GBC}$ together with the full comprehension scheme for all secondorder formulas. Beyond ${\rm KM}$ are theories which include choice principles for classes, such as the choice scheme and the dependent choice scheme. These theories have the advantage of biinterpretability with extensions of the wellunderstood firstorder set theory ${\rm ZFC}^_I$ (${\rm ZFC}$ without powerset and with the existence of the largest cardinal which is inaccessible). An even stronger principle, which endows classes with more setlike properties, is the existence of a canonically definable wellorder of the classes. The existence of a definable wellordering on classes makes it possible, for instance, to carry out the Boolean valued model forcing construction for class forcing notions (work in progress with Carolin Antos and SyDavid Friedman).
Are there natural secondorder settheoretic principles between ${\rm GBC}$ + $\Sigma^1_1$comprehension and ${\rm KM}?$ What natural principles lie beyond ${\rm KM}$ together with the choice scheme and the dependent choice scheme?
]]>The impediment to action advances action. What stands in the way becomes the way.
Catalog description: The real number system, completeness and compactness, sequences, continuity, foundations of the calculus.
]]>Don’t fear failure. Not failure, but low aim, is the crime. In great attempts it is glorious even to fail.
This quote appears on page 121 of Striking Thoughts: Bruce Lee’s Wisdom for Daily Living. For more great quotes, check out the Wikiquote page for Bruce Lee.
]]>The case for support document from my grant application gives details of this conjecture, its importance, and the strategies that I hope to employ to work on it.
Excitingly, the university has agreed to fund a PhD student as part of this research. I’ll post a brief description of what the PhD will focus on below. If you are interested, please get in touch!
]]>This programme of doctoral research is within the study of finite permutation group theory. Motivated by questions in model theory, about 20 years ago Cherlin introduced the notion of the relational complexity of a permutation group G; this is a positive integer which, roughly speaking, gives an indication of how easily the group G can act homogeneously on a relational structure. Cherlin’s conjecture concerns binary primitive permutation groups, i.e. primitive permutation groups which have relational complexity equal to 2. It is hoped that this conjecture might be proved in the next couple of years.
In light of this one naturally asks, next, whether we can classify groups with larger relational complexity, or whether we can calculate the relational complexity of important families of permutation groups. Calculating the relational complexity of a permutation group can be surprisingly tricky, so these sorts of questions can hide many mysteries!
In the process of working in this area, the student can expect to learn a great deal about the structure of finite simple groups (especially the simple classical groups) and, in particular, will study and make use of one of the most famous theorems in mathematics, the Classification of Finite Simple Groups.
]]>The mathematician does not study pure mathematics because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.
Joint work with Ari Meir Brodsky.
Abstract. Schimmerling asked whether $\square^*_\lambda$ together with GCH entails the existence of a $\lambda^+$Souslin tree, for a singular cardinal $\lambda$. Here, we provide an affirmative answer under the additional assumption that there exists a nonreflecting stationary subset of $E^{\lambda^+}_{\neq cf(\lambda)}$.
As a bonus, the outcome $\lambda^+$Souslin tree is moreover free.
Downloads:
Joint work with Gunter Fuchs.
Abstract. It is wellknown that the square principle $\square_\lambda$ entails the existence of a nonreflecting stationary subset of $\lambda^+$, whereas the weak square principle $\square^*_\lambda$ does not.
Here we show that if $\mu^{cf(\lambda)}<\lambda$ for all $\mu<\lambda$, then $\square^*_\lambda$ entails the existence of a nonreflecting stationary subset of $E^{\lambda^+}_{cf(\lambda)}$ in the forcing extension for adding a single Cohen subset of $\lambda^+$.
It follows that indestructible forms of simultaneous stationary reflection entail the failure of weak square. We demonstrate this by settling a question concerning the subcomplete forcing axiom (SCFA), proving that SCFA entails the failure of $\square^*_\lambda$ for every singular cardinal $\lambda$ of countable cofinality.
Downloads:
Citation information:
G. Fuchs and A. Rinot, Weak square and stationary reflection, Acta. Math. Hungar., 155(2): 393405, 2018.
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Six months after I had turned in my dissertation, I have finally received the approval on the damn thing. Continue reading...
]]>A student proposed to me the following strong form of König’s lemma:
Conjecture. Suppose that $G=(V,E)$ is a countable a graph, and there is a partition of $V$ into countably many pieces $V=\bigcup_{n<\omega}V_n$, such that:
Then there exists an infinite $K\subseteq V$ such that $[K]^2\subseteq E$.
In this post, I will quickly address this “conjecture”. Thus, if you prefer to think about it by yourself, read no more.
Refutation. Consider the graph $G=(\mathbb N,E)$ where $\{n,m\}\in E$ iff $n+m=1\pmod2$. It is easy to see that for every 3sized set $\{n,m,l\}$, we have $\{n,m,l\}^2\nsubseteq E$. On the other hand, letting $V_n:=\{2n,2n+1\}$ for all $n<\omega$ yields a partition satisfying the abovementioned properties.
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I gave an invited talk at the 14th International Workshop on Set Theory in Luminy in Marseille, October 2017.
Talk Title: Distributive Aronszajn trees
Abstract: It is wellknown that that the statement “all $\aleph_1$Aronszajn trees are special” is consistent with ZFC (Baumgartner, Malitz, and Reinhardt), and even with ZFC+GCH (Jensen). In contrast, BenDavid and Shelah proved that, assuming GCH, for every singular cardinal $\lambda$: if there exists a $\lambda^+$Aronszajn tree, then there exists a nonspecial one. Furthermore:
Theorem (BenDavid and Shelah, 1986). Assume GCH and that $\lambda$ is singular cardinal. If there exists a special $\lambda^+$Aronszajn tree, then there exists a $\lambda$distributive $\lambda^+$Aronszajn tree.
This suggests that following stronger statement:
Conjecture. Assume GCH and that $\lambda$ is a singular cardinal.
If there exists a $\lambda^+$Aronszajn tree, then there exists one which is $\lambda$distributive.
The assumption that there exists a $\lambda^+$Aronszajn tree is a very mild squarelike hypothesis (that is, $\square(\lambda^+,\lambda)$). In order to bloom a $\lambda$distributive tree from it, there is a need for a toolbox, each tool taking an abstract squarelike sequence and producing a sequence which is slightly better than the original one. For this, we introduce the monoid of postprocessing functions and study how it acts on the class of abstract square sequences. We establish that, assuming GCH, the monoid contains some very powerful functions. We also prove that the monoid is closed under various mixing operations.
This allows us to prove a theorem which is just one step away from verifying the conjecture:
Theorem 1. Assume GCH and that $\lambda$ is a singular cardinal.
If $\square(\lambda^+,<\lambda)$ holds, then there exists a $\lambda$distributive $\lambda^+$Aronszajn tree.
Another proof, involving a 5steps chain of applications of postprocessing functions, is of the following theorem.
Theorem 2. Assume GCH. If $\lambda$ is a singular cardinal and $\square(\lambda^+)$ holds, then there exists a $\lambda^+$Souslin tree which is coherent mod finite.
This is joint work with Ari Brodsky.
Downloads:
We survey the dynamics of functions in the EremenkoLyubich class, Among transcendental entire functions, those in this class have properties that make their dynamics markedly accessible to study. Many authors have worked in this field, and the dynamics of class functions is now particularly wellunderstood and welldeveloped. There are many striking and unexpected results. Several powerful tools and techniques have been developed to help progress this work. We consider the fundamentals of this field, review some of the most important results, techniques and ideas, and give steppingstones to deeper inquiry.
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As I wrote last time, the usual way to describe MathML's doublespec is this: Presentation MathML is for layout and Content MathML is for semantics.
Last time I wrote about how semantics are effectively absent from MathML on the web. Unfortunately, layout does not fare much better.
So at first the spec will tell you that's absolutely not true:
Presentation markup [...] is used to display mathematical expressions; and Content markup [...] is used to convey mathematical meaning.
So you will naturally start by thinking Presentation MathML is what you're after regarding equation layout (not mathematics).
The spec, however, throws you a curveball:
MathML presentation elements only recommend (i.e., do not require) specific ways of rendering; this is in order to allow for mediumdependent rendering and for individual preferences of style.
So Presentation MathML spec is about layout but not actually specifying how that should work.
This is obviously a problem when you want to see standardscompliant implementations in all major web browsers (even if it's just 4 engines). Usually (say with CSS or SVG), you can assume that a standard ensures developers that they are able to get consistent results across systems. Of course any standard will have gaps and edge cases but then, at least, specs can be clarified and either fixed in both standards and implementations or a standard can be identified as problematic (and ideally a less inconsistent standard can replace it).
However, this is not some kind of accident and you can easily find many statements in the same vein throughout the spec. For example, the section for <mfrac>
says effectively nothing about the spacing between numerator, fraction line, and denominator.
Or you get gems like this one from <mscarries>
This means that the second row, even if it does not draw, visually uses some (undefined by this specification) amount of space when displayed.
In contrast, start with any random part of contemporary CSS, e.g., flex container to start down the rabbit hole that are the result of quite meticulous discussions of layout specifics.
In other words, Presentation MathML does not even want to give you the same (messy) path to improvements as we're used to on the web (and we're still ignoring the practical problem that the Working Group is dead in the water so no fixes can be made).
At this point you might be wondering how that could be possible. After all, ther are plenty of equation rendering enginens out there that handle MathML. How do you reconcile this?
I think it is fairly simple (yet no less problematic). Presentation MathML assumes an implementor already knows how equation layout is supposed to work, in fact reading the spec you will get the feeling that it assumes you already have an equation layout engine at your disposal and you are merely adding MathML support, interpreting it in your engine.
in other words, Presentation MathML does not specify layout but is an abstraction layer, an exchange format for equation layout engines, a format that a rendering engine can (easily) make sense of within its already existing system.
(And yes, you could troll MathML enthusiasts by saying that Chrome and Edge support all layout requirements of the MathML spec. But please don't.)
Since I considered the value of Presentation MathML's semantics in the previous post, it's only prudent to double check the value of Content MathML for layout. Unsuprisingly, Content MathML really does not want to help either. The spec speaks quite clearly:
[...] encoding the underlying mathematical structure explicitly, without regard to how it is presented aurally or visually,
So no visual layout nowhere.
By the way, it seems easy to misunderstand this point in the spec. Of course we can render MathML content  lots of tools do. But what no tool can rely on is the MathML spec when it comes to deciding on how to render Content MathML content visually. As I already mentioned, few rendering engines are "MathMLbased" because they literally cannot be, they need to base their layout decisions on a more reliable source.
The other side of that coin is that you might disagree how to visually render Content MathML. In real life (at MathJax), we've actually had one or two complaints over the year how our ContenttoPresentation conversion is wrong
.
This is really just the core, the fundamental issue around MathML layout on the web. Even if you make the assumption that an equation layout engine should be added to browsers, there are more problems. And then we're still not talking about the problems of the shoddy implementations in Gecko and WebKit. Let's see if I'll get around to that. For now, let's continue the 10,000 ft view a bit longer.
]]>Peter Holy and Philipp Schlicht recently introduced a robust hierarchy of Ramseylike cardinals $\kappa$ using games in which player I plays an increasing sequence of $\kappa$models and player II responds by playing an increasing sequence of $M$ultrafilters for some cardinal $\alpha\leq\kappa$ many steps, with player II winning if she is able to continue finding the required filters [1]. The entire hierarchy sits below a measurable cardinal and intertwines with Ramsey cardinals, as well as the Ramseylike cardinals I introduced in [2]. The cardinals in the hierarchy can also be defined by the existence of the kinds of elementary embeddings characterizing Ramsey cardinals and other cardinals in that neighborhood. Before getting to their hierarchy and the filter games, we need some background.
Large cardinals $\kappa$ below a measurable cardinal tend to be characterized by the existence of certain elementary embeddings of weak $\kappa$models or $\kappa$models. A weak $\kappa$model is a transitive model of ${\rm ZFC}^$ of size $\kappa$ and height above $\kappa$, which we should think of as a miniuniverse of set theory; a $\kappa$model is additionally closed under $\lt\kappa$sequences. Given a weak $\kappa$model $M$, we call $U\subseteq P(\kappa)\cap M$ an $M$ultrafilter if the structure $\langle M,\in, U\rangle$ satisfies that $U$ is a normal ultrafilter. (Note that since an $M$ultrafilter is only $\lt\kappa$complete for sequences from $M$, the ultrapower by it need not be wellfounded.) Obviously, if the ultrapower of a weak $\kappa$model $M$ by an $M$ultrafilter on $\kappa$ is wellfounded, then we get an elementary embedding of $M$ into a transitive model $N$, and conversely if there is an elementary embedding $j:M\to N$ with $N$ transitive and critical point $\kappa$, then $U=\{A\in M\mid A\subseteq\kappa\text{ and }\kappa\in j(A)\}$ is an $M$ultrafilter with a wellfounded ultrapower. These types of elementary embeddings characterize, for instance, weakly compact cardinals. If $\kappa^{\lt\kappa}=\kappa$, then $\kappa$ is weakly compact whenever every $\kappa$model has an $M$ultrafilter on $\kappa$ (and hence a wellfounded ultrapower).
An $M$ultrafilter $U$, for a weak $\kappa$model $M$, is called weakly amenable if for every $X\in M$, which $M$ thinks has size $\kappa$, $X\cap U\in M$. Because a weakly amenable $M$ultrafilter is partially internal to $M$, we are able to define its iterates and iterate the ultrapower construction as we would do with a measure on $\kappa$. If $j:M\to N$ is the ultrapower by a weakly amenable $M$ultrafilter on $\kappa$, then $M$ and $N$ have the same subsets of $\kappa$, and conversely if $M$ and $N$ have the same subsets of $\kappa$ and $j:M\to N$ is an elementary embedding with critical point $\kappa$, then the induced $M$ultrafilter is weakly amenable. In a striking contrast with the characterization of weakly compact cardinals, it is inconsistent to assume that every $\kappa$model $M$ has a weakly amenable $M$ultrafilter! Looking at this from the perspective of the corresponding elementary embeddings $j:M\to N$, this happens because there is too much reflection between $M$ and $N$ for objects of size $\kappa$.
The existence of weakly amenable $M$ultrafilters for some weak $\kappa$models characterizes Ramsey cardinals. A cardinal $\kappa$ is Ramsey whenever every $A\subseteq\kappa$ is an element of a weak $\kappa$model $M$ which has a weakly amenable countably complete $M$ultrafilter. If we assume that every $A\subseteq\kappa$ is an element of a $\kappa$model $M$ which has such an $M$ultrafilter, then we get a stronger large cardinal notion, the strongly Ramsey cardinal. If we further assume that every $A\subseteq\kappa$ is an element of a $\kappa$model $M\prec H_{\kappa^+}$ for which there is such an $M$ultrafilter, then we get an even stronger notion, the super Ramsey cardinal. Both notions are still weaker than a measurable cardinal. If we instead weaken our requirements and assume that every $A\subseteq\kappa$ is an element of a weak $\kappa$model for which there is a weakly amenable $M$ultrafilter with a wellfounded ultrapower, we get a weakly Ramsey cardinal, which sits between ineffable and Ramsey cardinals. I introduced these notions and showed that a super Ramsey cardinal is a limit of strongly Ramsey cardinals, which is in turn a limit of Ramsey cardinals, which is in turn a limit of weakly Ramsey cardinals, which is in turn a limit of completely ineffable cardinals [bibcite key=gitman:ramsey]. I also called weakly Ramsey cardinals $1$iterable because they are the first step in a hierarchy of $\alpha$iterable cardinals for $\alpha\leq\omega_1$, which all sit below a Ramsey cardinal (see [bibcite key=gitman:welch] for definitions and properties). What happens if we consider intermediate versions between Ramsey and strongly Ramsey cardinals where we stratify the closure on the model $M$, considering models with $M^\alpha\subseteq M$ for cardinals $\alpha<\kappa$? What happens if we consider models $M\prec H_\theta$ for large $\theta$ and not just models $M\prec H_{\kappa^+}$?
Obviously we cannot have a weak $\kappa$model $M$ elementary in $H_\theta$ for $\theta>\kappa^+$. So let's drop the requirement of transitivity from the definition of a weak $\kappa$model, but only require that $\kappa+1\subseteq M$. Now it makes sense to ask for a weak $\kappa$model $M\prec H_\theta$ for arbitrarily large $\theta$. Suppose $\alpha\leq\kappa$ is a regular cardinal. Holy and Schlicht defined that $\kappa$ is $\alpha$Ramsey if for every $A\subseteq\kappa$ and arbitrarily large regular $\theta>\kappa$, there is a weak $\kappa$model $M\prec H_\theta$, closed under $\lt\alpha$sequences, with $A\in M$ for which there is a weakly amenable $M$ultrafilter on $\kappa$ (in the lone case $\alpha=\omega$, add that the ultrapower must be wellfounded) [1]. It is not difficult to see that it is equivalent to require that the models exist for all regular $\theta>\kappa$. Also, for a fixed $\theta$, it suffices to have a single such weak $\kappa$model $M\prec H_\theta$, meaning that the requirement that every $A$ is an element of such a model is superfluous. An $\omega$Ramsey cardinal is a limit of weakly Ramsey cardinals, and I showed that it is weaker than a 2iterable cardinal, and hence much weaker than a Ramsey cardinal. An $\omega_1$Ramsey cardinal is a limit of Ramsey cardinals. A $\kappa$Ramsey cardinal is a limit of super Ramsey cardinals. I will say where the strongly Ramsey cardinals fit in below.
It turns out that the $\alpha$Ramsey cardinals have a game theoretic characterization! To motivate it, let's consider the following natural strengthening of the characterization of weakly compact cardinals. Suppose that whenever $M$ is a weak $\kappa$model, $F$ is an $M$ultrafilter and $N$ is another weak $\kappa$model extending $M$, then we can find an $N$ultrafilter $\bar F\supseteq F$. What is the strength of this property? I showed that it is inconsistent. Roughly, it implies the existence of too many weakly amenable $M$ultrafilters, which we already saw leads to inconsistency (see [1] for proof). So here is instead a game version of extending models and filters formulated by Holy and Schlicht.
Let us say that a filter is any subset of $P(\kappa)$ with the property that the intersection of any finite number of its elements has size $\kappa$. We will say that a filter $F$ measures $A\subseteq \kappa$ if $A\in F$ or $\kappa\setminus A\in F$ and we will say that $F$ measures $X\subseteq P(\kappa)$ if $F$ measures all $A\in X$. If $M$ is a weak $\kappa$model, we will say that a filter $F$ is $M$normal if $F\cap M$ is an $M$ultrafilter.
Suppose $\kappa$ is weakly compact. Given an ordinal $\alpha\leq\kappa^+$ and a regular $\theta>\kappa$, consider the following twoplayer game of perfect information $G^\theta_\alpha(\kappa)$. Two players, the challenger and the judge, take turns to play $\subseteq$increasing sequences $\langle M_\gamma\mid \gamma<\alpha\rangle$ of $\kappa$models, and $\langle F_\gamma\mid\gamma<\alpha\rangle$ of filters on $\kappa$, such that the following hold for every $\gamma<\alpha$.
Holy and Schlicht showed that if the challenger has a winning strategy in $G^\theta_\alpha(\kappa)$ for a single $\theta$, then the challenger has a winning strategy for all $\theta$, and similarly for the judge. Thus, we will say that $\kappa$ has the $\alpha$filter property if the challenger has no winning strategy in the game $G^\theta_\alpha(\kappa)$ for some (all) regular $\theta>\kappa$. [1]
Holy and Schlicht showed that for regular $\alpha>\omega$, $\kappa$ has the $\alpha$filter property if and only if $\kappa$ is $\alpha$Ramsey! Using the game characterization, they showed that $\kappa$ is $\alpha$Ramsey ($\alpha>\omega$) if and only if every $A\in H_{2^{\kappa^+}}$ is an element of a weak $\kappa$model $M\prec H_{2^{\kappa^+}}$, closed under $\lt\alpha$sequences, for which there is an $M$ultrafilter. [bibcite key=HolySchlicht:HierarchyRamseyLikeCardinals] Thus, we actually only need a single $\theta=2^{\kappa^+}$! So instead of $H_{\kappa^+}$ as in the definition of super Ramsey cardinals, the natural stopping point is $H_{2^{\kappa^+}}$. With the new characterization, we can also show that a strongly Ramsey cardinal is a limit of $\alpha$Ramsey cardinals for every $\alpha<\kappa$.
So now we have in order of increasing strength: weakly Ramsey, $\omega$Ramsey, $\alpha$iterable for $2\leq\alpha\leq\omega_1$, Ramsey, $\alpha$Ramsey for $\omega_1\leq\alpha<\kappa$, strongly Ramsey, super Ramsey, $\kappa$Ramsey, measurable.
Why the restriction $\gamma>\omega$? I showed that an $\omega$Ramsey cardinal is a limit of cardinals with the $\omega$filter property (see [bibcite key=HolySchlicht:HierarchyRamseyLikeCardinals] for proof). The problem arises because even if the judge wins the game $G^\theta_\omega(\kappa)$, the ultrapower of $M_\omega$ by $F_\omega$ need not be wellfounded. The same problem arises for any singular cardinal of cofinality $\omega$. The solution seems to be to consider a stronger version of the game for cardinals $\alpha$ of cofinality $\omega$, where it is required that the final filter $F_\alpha$ produces a wellfounded ultrapower. Let's call this game $wfG^\theta_\alpha(\kappa)$. The wellfounded games don't seem to behave as nicely as $G^\theta_\alpha(\kappa)$. For instance, it is not known whether having a winning strategy for a single $\theta$ is equivalent to having a winning strategy for all $\theta$. I conjecture that it is not the case. Still with the wellfounded games, the arguments now generalize to show that $\kappa$ is $\omega$Ramsey if and only if $\kappa$ has the wellfounded $\omega$filter property for every $\theta$.
Finally, what about $\alpha$Ramsey cardinals for singular $\alpha$? Well, since a weak $\kappa$model $M$ that is closed under $\lt\alpha$sequences for a singular $\alpha$ is also closed under $\lt\alpha^+$sequences, $\alpha$Ramsey for a singular $\alpha$ implies $\alpha^+$Ramsey. So instead Holy and Schlicht defined that $\kappa$ is $\alpha$Ramsey for a singular $\alpha$ if $\kappa$ has the wellfounded $\alpha$filter property (the wellfounded part is only needed for $\alpha$ of cofinality $\omega$) [1]. Now we have the $\alpha$Ramsey hierarchy for all cardinals $\alpha\leq\kappa$. Holy and Schlicht showed that this is a strict hierarchy of large cardinal notions: if $\kappa$ is $\alpha$Ramsey and $\beta<\alpha$, then $V_\kappa$ is a model of proper class many $\beta$Ramsey cardinals, and moreover if $\beta$ is regular, then $\kappa$ is indeed a limit of $\beta$Ramsey cardinals [1].
Here is the video: Continue reading...
]]>Yet, the fact that mathematical objects are real is the daily experience of mathematicians (though few would ever claim this, because they are much too cautious). I’d like to try to explain this experience. Since I am not a philosopher, there will be no robust philosophical arguments. I will not discuss ontology. Try not to be disappointed.
Imagine you were an astronomer. (No, go on. Give it a go.) You point your telescope up in the air and – lo – a new star appears. You call a friend, and tell her the news. She points her telescope in the same place and – lo – the same star. You write up your discovery, and a team of astronomers in Belgium train their more powerful telescopes on the same spot, and describe the colour and size of the star. You have another look, and see they are correct. An international team in Chile use radioastronomy to discover that your star is actually two stars, orbiting around each other. It is later discovered that there is a large exoplanet orbiting one of these stars.
Now – I guess – it could be argued that there is no star. It could be argued that you invented it, and then let everyone else know how to do the same. The star is some sort of socially constructed illusion. In my view this is a purest nonsense. There is a real star, it is really out there. That, after all, is the belief of (most) astronomers. Otherwise, we might as well give up the whole astronomy thing altogether.
So I am getting to my point. Thanks for being patient.
My point is that this is also the daily experience of mathematicians. Let’s suppose I am studying transcendental dynamics (as I do), and I study a new set which seems of interest (well, you never know). I email a colleague, and they confirm the set looks as I said, and maybe they spot something else; perhaps it has dimension one, or is dense in the plane, or something technical like that. We write a paper. A team of Belgian mathematicians read our paper, and note that, in fact, our set has other interesting properties. They email us and we find that this is indeed the case. More papers follow, and then someone (in Chile, perhaps) observes that our set is actually the union of two interesting sets, and gives some further properties of each. When we look into it, we see that this is indeed the case. This is how (pure) maths is done.
Essentially this story (for it is a story; I have not discovered any sets of interest to Belgians) is no different to the story about the star. And it is very difficult not to believe the punchline is the same; the set exists ‘outside our heads’, just as the star exists ‘outside the heads of the astronomers’. (I’m not trying to claim mathematical proof here; I’m just trying to communicate how it feels to do mathematics).
A reallife example of this story is the famous Mandelbrot set. This was first discovered in the 1970s, when it was very difficult to draw a picture of it. But mathematician talked unto mathematician, and more and more properties were discovered. Technology has moved on, and now highly detailed pictures exist. It is a remarkable object: for example, the set is so intricate that if you try to draw a line around the edge, you will find that your ‘line’ is actually twodimensional. It is even more intricate than the coast of Norway. Nonetheless, all mathematicians would agree they have been studying ‘the same thing’ all this time.
So it seems undoubtedly true that mathematical objects exist. I am as confident in the existence of the Mandelbrot set, or the sine function, or Riemann surfaces of genus zero as I am in the existence of Belgium. When we study mathematical objects, we discover them – we do not invent them. There are thing that exist that are not material objects.
You may feel that this is silly, because if they exist, then where is their home? (It is probably not Belgium). How do we see them? What are they made of? These are a good questions.
]]>
This one's slightly tricky. And I also have a confession to make. In the first two parts I pretended I've written about MathML when I really only wrote with half of it in mind.
One problem of the MathML spec in general is that it's really two, quite distinct specs: Presentation MathML and Content MathML.
Now the common description is: Presentation describes layout and Content describes semantics. I think one of the problems for MathML in general is that it is not that easy.
So obviously that's wrong. After all there is Content MathML and it specifies an enormous amount of semantics. Such an enormous amount actually that you can express lambda calculus. You also get a whole bunch of fantastic elements (for <reals>
) and on top of that builtin, infinite extensibility via content dictionaries. So you can do quite literally everything in Content MathML.
So what's the problem?
It's the simplest and most practical problem: Content MathML plays no significant role in real world documents. You can find it in niche projects (such as NISTS's handcrafted DLMF), you can find it hidden in commercial enclosures (such as Pearson's assessment system where I wonder why you'd need its expressiveness), you can also get it by exportig it from computational tools (Maple, Mathematica etc.). But in real world documents, it's nonexistent.
I can't really tell you why that is. Perhaps like most formal abstractions of mathematical knowledge, it ignores the practicalities of humans communicating knowledge. Perhaps, when it comes to its computational prowess, it probably fails on the web because it cannot compete with the practicality of JavaScript or serverbased computation (à la Jupyter Notebooks).
I also have heard repeatedly that it's simply too difficult to create. And from my limited experience with MathJax users it doesn't help that the spec itself warns people that it encodes structure without regard to how it is presented aurally or visually
, i.e., it's sometimes not clear how Content MathML should be rendered.
Ultimately, lack of content (pardon the pun) makes Content MathML of little relevance on the web. (An interesting but separate question might be whether the way Content MathML expresses semantics fits into the style that HTML has adopted in recent years; another time perhaps.)
But there's actually a second problem for MathML and semantics on the web here: Presentation MathML.
It's easy to think that Presentation MathML specifies at least some semantics. And if it specifies some, maybe it's a good basis to build upon. After all, how semantic was HTML really, back in the day?
For example, there's the <mfrac>
element and you might think it specifies a fraction. Unfortunately, you'd be wrong. The spec itself speaks of fractionlike objects such as binomial coefficients and Legendre symbol
which are about as far from fractions as you can think of. Of course you can find even more egregious examples in the wild such as plain vectors encoded with mfrac
. Similarly, <msqrt>
does not represent square root but root without index and it is used accordingly in the wild (while <mroot><mrow>...</mrow><none/></mroot>
constructions are practically unheard of).
The point is that you can't complain about some kind of abuse of markup because Presentation MathML does not make this kind of a distinction.
Now for a long time, I thought there might just be enough semantics in Presentation MathML to get away with. Working with Volker Sorge and his speechruleengine and integrating SRE's semantic analysis into MathJax meant a deep dive into what kind o structure you can find in Presentation MathML. And as amazing as its heuristics are, it becomes clear how brittle they remain and how quickly you find (real world) examples that break things. This isn't to say you can't guess the meaning of a large selection of real world content. It just makes it clear that you are working with a format void of semantic information. (And we're not talking about tricking machine learning models here, just run of the mill content.)
When you get down to it, I would say that there are effectively only two elements in Presentation MathML that appear reliably semantic in the real world: <mn>
and <mroot>
. And even these examples are stretching it. For for the former, the spec suggests that <mn>twenty one</mn>
is sensible markup. For the latter, it seems to be mostly accidental that roots simply haven't been sufficiently abused in the literature (yet) and thereby retain a unique place of being a visual layout feature that is used consistently to describe (many different concepts of) "rootness". (For the record, there's also <merror>
which is pretty solid, semantically speaking; just not very mathematical.)
There are other, more indirect signs of the failure of MathML to specify semantics. For example the absence of typical benefits of semantic content such as usable search engines or knowledge management tools. But that's a very different problem to discuss.
Anyway, so MathML that specifies semantics could exist but does not. On to layout.
]]>One advantage of MathML on the web is that it's XML, i.e., it looks a lot like HTML and SVG and does not require a lot of extra tooling (e.g., parsers). In addition since you can preserve its structure when converting to HTML or SVG, you can can hack MathML markup to improve the result on the web, e.g., by adding CSS or ARIA.
Still, being XML is obviously not enough to make anything a good web standard.
Obviously this depends a lot on what qualities you are after but I've found it to be a common misconception that MathML is somehow universally superior to other ways of marking up equations. That misconception is getting it backwards.
Like any exchange format, MathML's design is more that of a least common denominator between document systems and, in particular, between visual rendering engines for equational content. By definition, this means it is the least expressive, least flexible, and least powerful format.
A good exchange format would of course be a great thing to have and it can still be very powerful if the ecosystem's diversity is not too great. Unfortunately, that's not the case for MathML where rendering engines for equational content exist and vary considerably between ancients like troff or TeX, modern word processors, computer algebra systems, and more.
So while it is easy to create MathML from other equation input formats it is effectively dumbed down in the process. Reversely, it is not easily interpreted in another system without significant loss of information. This is of course nothing special, just look at binary image formats or text processing. But this is a problem for MathML because it is designed for this purpose; however, it neither reaches the quality of, say, SVG as an exchange for vector graphics, nor does it provide reallife advantages over, say, subsets of LaTeX notation (e.g., in jats4reuse) or even ASCIIstyle notation.
A particular example of this loss of information is that importing MathML into other systems, while often possible, is rarely reusable. This is a bit like importing a binary image format into another editor; yes it works, but there are limits to how well you can edit the import without redoing the whole thing. To give a simple example, David Carlisle's pmml2tex provides perfectly nice visual output in print but rather unusual TeX markup.
The fact that after 20 years there are virtually no rendering systems out there that use MathML internally indicates that MathML fails to provide a decent solution for another basic use case.
After these basic, to some degree social problems, let's talk about core problems of the spec itself next.
]]>And that was fine. All three options are roughly equivalent, in the sense that they present you the material in a very structured way (or they at least intend to). You don't reach the definition of \(\aleph_0\) because you defined what is equipotency and cardinality. You don't reach the definition of a derivative before you have some semblance of notion of continuity. Knowledge was built in a very structural way. Sometimes you use crutches (e.g. some naive understanding of the natural numbers before you formally introduce them later on as finite ordinals), but for the most part there is a method to the madness. Continue reading...
]]>After finishing MathML as a failed web standard last year, I've been meaning to write a followup to discuss fundamental issues I see with MathML as a web standard. I found it very difficult, even painful to do so. Over the past few years I realized that most people simply don't know much about both MathML and modern web technology. I don't claim I'm a great expert myself but running MathJax for the past 5 years has given me some ideas.
Caveat Emptor. The problems I hope to outline may seem to be a general rejection of MathML as a whole; that's not what I'm after. It'd actually be silly to try to bash MathML because it is simply too successful. I also actually kind of like MathML, despite its many horrors; I think it was a great idea 20 years ago and it's still useful to hack it to get to better things.
Primarily, what follows is the result of me trying to understand why MathML failed on the web. I think there are a few key reasons for its failure. My motivation is to form an opinion on whether MathML is salvageable as a web standard or fundamentally unfit to be part of today's web technology (and should then best be deprecated).
The success outside of the web is an important factor as it limits how much MathML can realistic change. So let's start there.
MathML is the dominant format for storing equations in XML document workflows today. It's a reasonable assumption that the vast majority of equational content today is available in (or ready to convert to) MathML: virtually all STEM publishers use MathML in their workflows, major tools like Microsoft Word (favored throughout education) use formats intentionally close to MathML, and most other forms of equation input can be converted more or less easily.
MathML has a long history as a W3C standard and it's natural to think that MathML's success is somehow connected to the web's success.
However, that's not the case (except perhaps by making an ultimately empty promise). The<math>
tag was first proposed in HTML 3.0 in 1995 but was remove from HTML 3.2 in 1997. It was transformed into one of the first XML applications and MathML was born in 1998 and lived in XML/XHTML limbo for the next decade. Finally, MathML returned to HTML proper with HTML 5 in 2014.
It should seem obvious that because MathML was not part of HTML (or any other web standard implemented by browsers), it could not have succeeded because of the web's success. Instead, it was MathML's success outside of the web that allowed it to survive and eventually make it back into HTML5.
So there naturally was a disconnect. Unfortunately, even when MathML came back in HTML5, that disconnect remained effectively unchanged. A simple example is the timeline. MathML 3's first public working draft was published in 2007, the year HTML WG was just being rechartered to bring together HTML5 (which took 7 years). The difference between the early working drafts of MathML 3 and the eventual REC (in 2010) seems to include little fundamental change (lots of details being hashed out but the core seems in place pretty early on). Only a handful of changes were made between 2010 and 2016 (when the Math Working Group shut down). It seems only mild hyperbole to say that MathML 3 was effectively done before the HTML5 was really getting started.
Overall, it seems clear from the various specs that the return to HTML5 had not much influence on MathML — or vice versa. For example, there is no hint of giving MathML the "CSS treatment" that HTML got (e.g., clarifying HTML layouts like tables via CSS) nor is there a sign that HTML and CSS ever considered what MathML brought to the table in terms of semantics and layout. This disconnect (and the lack of interest in overcoming it later on) is likely the root cause for MathML's failure.
I think one of the reasons why this disconnect was not overcome is the success of MathML and where that success occurred.
If you speak to early adopters of MathML, you will notice that MathML's success was due to its efficacy in print workflows (with rendering to binary images perhaps being a nice extra in the pitch). That's what XML workflows were producing and while the web was a nice thing to hope for, if MathML hadn't done a good job in print, it would not have gone anywhere in XMLland. This also means that MathML suffers from the general problem of equational content (shameless selfplug).
I suspect this success made the MathML community a bit blind to the fact that the web platform was moving away from any common ancestry there may have been, especially on the implementation level but perhaps more importantly in terms of being a rapidly growing technology being practiced by a similarly growing group of specialists (aka web developers).
A sign of this effect is that (especially among nonexperts) it seems many people confused the hopes of MathML in HTML5 with a promise and in extreme cases some sort of moral obligation for browser vendors to implement MathML support natively. In retrospect, I think there may have been a short window where things could have turned out differently (and I hope I'll get to that idea later on). More likely, my brain is playing tricks on me because I shared that hope.
In any case I find the history to be rather odd, overall. A failed web standard became successful in print production and that success was so significant that it was reintroduced to HTML.
What I think is often missed when discussing MathML is how the success outside the web took its toll on the MathML specification. Its development was focused almost entirely on legacy (print) content and completely detached from the direction random twists and turns of the more successful web standards (first and foremost HTML and CSS). Still, MathML neither tried to align its own direction with the platform nor did it try to take inspiration or to influence those developments.
Finally, I think the particulars of print (and image) rendering of MathML has produced a crucial misconception about MathML: the fact that MathML works well in those settings does not imply that MathML works well as a web technology.
Next I'll try to step a bit back and maybe talk about some of the basics of the spec.
]]>There is still much work to be done. The main work to be done has to do with comments. Currently, there is no way to comment on posts here. Indeed, since this is a static site, dynamic features like comments are not available straight out of the box. An indirect consequence of this is that old comments haven’t been migrated from WordPress. I’m keeping the old WordPress site alive in its current state until comments have been migrated.
Another item to do is to integrate the new site into Boole’s Rings. Currently, most of the Boole’s Rings sites are WordPress based. Peter Krautzberger moved to GitHub Pages a two years ago; it seems from my current experience that migrating is much easier now. I don’t know how well integration will work but the experiment itself is well within the spirit of Boole’s Rings.
These next steps will happen over the next weeks (… or months! … or years?) In the mean time, there are a few small intermediate steps like setting up a custom domain name. Anyway, you can track my progress on GitHub…
]]>Joint work with Chris LambieHanson.
Abstract. We derive a forcing axiom from the conjunction of square and diamond, and present a few applications, primary among them being the existence of superSouslin trees.
It follows that for every uncountable cardinal $\lambda$, if $\lambda^{++}$ is not a Mahlo cardinal in Godel’s constructible universe, then $2^\lambda = \lambda^+$ entails the existence of a $\lambda^+$complete $\lambda^{++}$Souslin tree.
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When I look back at some of the proofs I wrote when I started work on my PhD, I realise how much I have learned. My supervisors – who were very gracious, very helpful, and very dedicated – used to cover my early work in red ink. I then learned how to write a proof through an iterative (and very painful) process, in which I would write something, receive the red ink, fix those problems, receive further red ink, and so on. I became very familiar with red ink. Very, very familiar.
In this note I’d like to comment on how one might spot problems oneself, rather than depend on one’s supervisors in this way. This is not a trivial task, but a really important one. Perhaps I can offer a few pointers which might be of help.
Let’s suppose you have proved a result. You’ve written it all up to your own satisfaction, and wish to share your achievement with your fellows. I began to make a list of the things you should do, but it was very long, exceedingly tedious, and all boiled down to the word check. Which is a bit boring. So let’s try the following, which is less prescriptive if possibly less allencompassing. It’s just three words. How hard could that be?
First forget. In developing your proof you, no doubt, came up with all sorts of ideas and intuitions and implications and pictures. You have to (somehow) now lay these all to one side. Your reader will not have any of this in front of them, so you have to be sure that none of your work now depends or uses anything other than the words in front of you. (Incidentally, the best way to do this is to put your proof to one side for a few months, and then come back to it. You’ll be astonished how terrible it will look).
Second focus. Focus on the words in front of you, and what they say. This is easier said than done; because you expect your words to say one thing, you will tend to interpret them in that way. Try not to. Look at what is written and nothing else.
Third check. Read what you have written, word by word, sentence by sentence, and ask yourself the question “why on earth does that follow?” Notice the negation; if you expect things to be wrong you are more likely to spot mistakes than if you expect them to be correct. In my personal experience they are probably incorrect.
I could probably make a list of common mistakes, but it really is hard to make that interesting. So I will highlight just three (three is a useful number here):
The word “clearly”: It is very easy to make the mistake of writing “clearly XYZ” when what you mean is “XYZ seems pretty darned obvious to me but I can’t quite work out why”. If you can’t work out why XYZ is true, chance is that is isn’t.
Things that are true but don’t actually follow: This is a very easy mistake to make; you write something like “Since X, then Y” and assume it is OK because Y really is true. But you are not asserting here that Y is true, and that is not what you need to check. You need to check that Y follows from X and nothing else!
Failure to satisfy all necessary conditions: If you use another result (maybe a book result, or a lemma of your own from earlier) you need to be sure that all the conditions are checked. This is especially true of a book result – if that says something like “If A, B, C, D and E, then F”, then there is no chance to use this result if only A, B, C and D are true.
Yes, this is all amazingly tedious. Yes, this is a very lengthy process. No, there is no alternative (apart from asking a friend to check). Yes, you will be a better mathematician when you can do all this. No, I do not claim to be able to do this all the time myself. Yes, I welcome feedback and other suggestions.
]]>Hamkins' multiverse is essentially taking a very illfounded model and closing it to forcing extensions, thus obtaining a multiverse which is more of a philosophical justification, for example every model is a countable model in another one, and every model is illfounded by the view of another model. The problem with this multiverse is that if we remove the requirement for genericity, then everything else can be satisfied by the same model. Namely, \(\{(M,E)\}\) would be an entire multiverse. That's quite silly. Moreover, we sort of give up on a concrete notion of natural numbers that way, and this seems a bit... off putting. Continue reading...
]]>When people speak about math content in the context of the web they usually mean equational content (or simply equations). That is, they don't mean content in a mathematical field (which often enough does not qualify as equations), they simply mean something that looks like an equation.
Now you might argue that an equation in physics is still basically mathematical content but in reality both mathematician and physicist will frequently disagree with you (and each other, possibly explosively so). You quickly get to the edge when considering chemical equations and if you want to classify the nonsense notations in the life sciences you might question your sanity.
It's not hard to understand why this is. For example, most typesetting tools with support for equations will have some kind of math mode for them. But I think it's worth while differentiating the two so I'll try my best to stick to equational content. On the one hand, the importance of math on the web is often exaggerated because it is really nonmathematical equational content that's the majority (and even that is a blip on the radar). On the other hand, it does not help to confuse a field of study with what effectively comes down to a layout tradition.
Also, sorrynotsorry for misleading you with the title here.
The fundamental problem of equational content is that, well, that it's simply pretty terrible all around. It's convoluted,extremely compressed, archaic, and generally undecipherable. It destroys academic careers by the millions and it can often only be understood when you can see it written live (i.e., animated). At its best equations are like good abstract drawings, at worst (usually?) they're deafening gibberish.
Stray thoughts.
One. I always thought Bret Victor's (in)famous Kill math was largely wrong about the specifics of his criticism (for one, he seems to dismiss the incredible power of compression that differential equations exhibit  along with the obvious problems that stem from compression). But he is of course utterly right with his incredible work exploring how modern media like the web allow for a much richer expression of human thought, one that opens the content up to more people, often by adding means of interacting with it, especially means for untrained people (like tiny humans).
Two. Every once in a while I've wondered: what if Tim BernersLee had given the web some basic building blocks for equations. Just a fraction and a square root; maybe instead of image renditions of print equations we'd have immediately seen the same creativity applied to equations as there was with hacking general layout (1px GIF anyone?). Of course, that's hopelessly romanticizing the evolution of the web. Why can't I stop wondering.
Three. On and off (and I've come full circle on this several times) I've wondered whether math is ahead of other sciences on the web. I mean the <math>
tag was proposed in fricking HTML 3. So is math ahead? Maybe. But then why is scientific content so much more vibrant and transformative on the web compared to math?
The most obvious flaw of equational content is that it's deeply rooted in print. Given the limitations of print technology, equational content has needed to adopt bad practices for such a long time that many people consider them good.
I'm not (just) thinking about the problem of general comprehension as it is too tainted by poorly trained practitioners on all levels. Sure, equational content is often more difficult to parse than necessary but that's not different from poorly phrased prose.
The main problem is the tradition of abusing print technology to get more and more variations of notation squeezed into the medium. The constant abuse of sub and superscripts is a great example; if you need to add a variant of an object you've already introduced in your notation, just slap some sub/superscripts around it, et voilà, a new object.
The abuse of letters with different fonts is another horror in equational content. If you have ever run into a paper where a dozen variations of G
appear, denoting a convoluted set of somewhat related concepts, you'll know this horror well. Unbelievably enough, Unicode has deemed this abuse of notation important enough that we now have such wonders as the Unicode point mathematical bold italic G in the Mathematical Alphanumeric Symbols
Block.
Another historic accident are stylistic separations. For example, in print it's abhorred to make math content bold when the surrounding content is bold (e.g., in a heading) yet on the web people complain that an equation in a link doesn't get the correct text decoration (what would that be??).
Obviously, there's little point in criticizing the historic development of equational content. Given that print was mostly limited to (at best) grayscale with a limited character set, naturally people had to be creative. It is amazing what this accomplished.
The real problem comes up when pretending that this tradition should do more than vaguely inform a medium such as the web. The web so far developed without much influence from equational content. It has adopted a rather different approach to separating content and presentation and the traditions of equational content are essentially incompatible with the web's approach.
I can find no argument for why the web stack should bend over backwards to accommodate these mostly quite bad traditions of equational content for print. This is perhaps similar to the situation of CSS paged media.
Obviously, it's not like you shouldn't be able to put traditional equational content on the web  you should (and you can very well today). But I've come to think it's perfectly fine, in fact, it is appropriate that this continues to be a difficult problem. For example, traditional equational content is almost always inaccessible (without heuristic algorithms, i.e., guessing around); it's basically a bunch of glyphs placed in a weird 2D patterns (like above and below a line which in turn is magically centered on some baseline and may or may not indicate it corresponds to the notion of a mathematical fraction). Pretending that this is a basis for accessible rendering on the web strikes me as foolish (or ridiculously zealous).
If you think that all equational content should be limited to the traditions of the print era, fine. I think humanity can do better on the web. Though I think we would need to acknowledge that the (print) traditions enshrined in equational content are flawed and should (and invariably will) be replaced with better concepts and narratives that are appropriate for this medium.
]]>I gave a 3lecture tutorial at the 6th European Set Theory Conference in Budapest, July 2017.
Title: Strong colorings and their applications.
Abstract. Consider the following questions.
It turns out that all of the above questions can be decided (in one way), provided that there exists a certain “strong coloring” (or “wild partition”) of a corresponding uncountable graph.
In this tutorial, we shall present some of the techniques involved in constructing such strong colorings, and demonstrate how partial orders/topological spaces/algebraic structures may be derived from these colorings.
Lecture 1 ** Lecture 2 ** Lecture 3
]]>
There is a nontrivial percentage of the population which have some sort of color vision deficiency. Myself included. Statistically, I believe, if you have 20 male participants, then one of them is likely to have some sort of color vision issues. Add this to the fairly imperfect color fidelity of most projectors, and you get something that can be problematic. Continue reading...
]]>Still, the things you can do well, you obviously should. And yet, every once in a while, somebody throws you a curveball and you just have to shout: This is why we can't have good things!
.
The other day on a client project, the QA specialist pointed out that the content was consistently using <em>
where it should be using <i>
. Can we fix that?
The semantics of these and related HTML5 tags is a bit subtle, but there is a difference and it should be easy to just replace one with the other, right? Right? Famous last words.
At first sight, this was easy. The HTML came out of some JATSlike XML, which was using <italic>
elements. So map to <i>
, right? But hold on, you'll say, HTML5 reinterpreted <i>
to no longer indicate layout but semantics; it now indicates a change of voice. Unfortunately, JATS's <italic>
is focused on the typographic aspects, so it does not really help. The again, it could help a little bit more because <italic>
allows for a toggle
attribute to indicate emphasis. Sadly, the actual XML did not provide that information.
Since the piece of the tool chain that turned <italic>
into <em>
was actually my doing, I was clearly at fault. However, I had my reasons. Namely, that all of this came from a LaTeX source and in this real world LaTeX content, \emph{}
and its brethren were the dominant source for <italic>
. So clearly that should be <em>
in the end?
Now of course, almost all LaTeX authors don't give a damn beyond getting that PDF to look how they want it, so while they mostly use \emph{}
like macros, they mix it freely (and inconsistently) with \textit{}
and its brethren. So the conversion (written by an absolute expert) rightly says screw it, all I can say is it wants italics here
, thus merging them both together.
It's my job to dig deeper than that so I took the time to look through the actual content available. Not the TeX, not the XML but the actual writing.
Lo and behold, the actual text use is pretty different: by far, most occurrences of <em>
happened in the context of quick, inline definitions. Invariably, you find these in introductions of mathematical research articles where you include commonly known definitions from a field so as not to cause bloat (because publishers and editorial boards continue to care more about page numbers than well documented research results).
A definition does not really fit either <i>
or <em>
. The closest you get in the spec, is an example of using <i>
to reference a past definition.
<p>The term <i>prose content</i> is defined above.</p>
To make matters worse, there is of course an entirely different element that fits perfectly:
The
<dfn>
element represents the defining instance of a term.
Perfect match for the vast majority of the content in question. So we should switch everything over, right?
The answer is, of course, no. Not because some content would end up with the wrong semantics (scroll to top) but because that was not the only use I found: almost without exception, the samples includes the use as a definition alongside the use as <em>
or <i>
.
And that is why we can't have good things.
All of this is about as surprising as finding a handwritten table of contents in a Word document. TeX is for print layout and font styles are used for all manners of cruelty. The question I had to answer with my client was: can we do anything about it?
In the end, beauty lies in the eye of the beholder and semantics in the eyes of the reader. We did, in fact, switch to <i>
with the plan to expose more information from the original source regarding emphasis so we can gather more data on its usage. Fundamentally, this won't help because it doesn't solve the problem of inline definitions. Still, some analysis might reveal pragmatic improvements down the line.
In the end, it's not hard to argue that a definition that is well known in the field and that is done inline in the introduction of an article is more like the kind of reference to a definition as in the above example from the spec (in fact, often enough it is done in the vicinity of a bibliographic reference). Of course, we're still conflating \emph
and \textit
.
Now zealots idealists will argue that authors "just" have to learn to use semantic macros in TeX. After all, there are plenty of "semantic" LaTeX packages out there; just start writing good markup already!
Besides the lack of pragmatism, the only viable solution I can see would be a LaTeX package matching specifically HTML5 markup. After all, we have the tags and they have established definitions; any "semantics" beyond that will only cause issues down the line (what if a tag is introduced to HTML but with a slightly different meaning?). Even then, it doesn't solve the social problem at the heart of so many publishing technology issues: who would make the effort and use it? It's extra work and does nothing for print; why would an author do extra work when they think print rules?
I think only someone interested in creating HTML output would make the effort. And at that point you have to ask: Why would those authors bother with an archaic programming language like TeX to write HTML? They will find it invariably easier to just write HTML or their favorite lightweight markup for creating HTML, especially given the speed at which HTMLtoPDF solutions are improving). Building tools for LaTeX to solve this would just create extra work but help nobody. Just build better tools for writing HTML.
Doch das ist eine andere Geschichte und soll ein andermal erzählt werden.
]]>This past semester I taught the course for the second time. You can find the syllabus, list of problems, etc. for the Spring 2017 semester by going here. On the students’ final exam, I asked them which problem was their favorite from the semester. Below is the list of problems that they mentioned including the number of votes that each received. The level of difficulty of the problems covers the spectrum. Some of these are not easy. Have fun playing!
A while back I wrote a similar post that highlighted 15 fun problems from the first time I taught the course. You’ll notice that there is some overlap between the two lists.
]]>As tradition decrees, we shall begin our show by taking a closer look at our number.
146 is an octahedral number (and thus a figurate number).
Even more amazingly 146 is an untouchable number which means it cannot be expressed as the sum of all the proper divisors of any positive integer (including itself). Can you guess how many untouchable numbers there are? Of course, infinitely many and, of course, this was first proved by Paul Erdős. But did you know that the only known proof that 5 is the only odd untouchable number depends on a stronger version of the Goldbach conjecture? Amazing!
Now that you've warmed up, let us enter the magnificent, magnetic madness of the mathematical blogging carnival.
If you have any affinity to football (the real kind, not the funny American stuff), then start off with Nira Chamberlain who reviews the mathematical simulation model he built for his favorite team  you know, like any normal awesome football fan would do.
Next, follow Sean and Jamidi to the depths of the chalkdust magazine where they spoke with one of the great mathematical storytellers, Marcus du Sautoy.
Beware now, lest you be pulled into the enchanted world of The Mathemactivist who can draw a Hilbert Curve by hand.
Come now, and follow us to the trickster's lair where Tom rocks math takes a closer look at three fun numbers to tell you things you didn't realize you ever wanted to know. From here, follow us to the depth of the mathvault and let Scott Hartshorn lure you with an introduction to statistical significance after which all your papernerd needs will be met by Nick Higham, who looks at the benefits of dot grid paper (including, of course, a LaTeX template).
Before you leave, be sure to witness the spectacle of John Cook taming the Weibull distribution and connecting it with Benford’s law. And as an encore, John will take you far from the equation systems you solved in algebra when you were a kid to the "simple" generalization that can be solved using a Gröbner basis (which, as so many things in mathematics, were not actually discovered by Gröbner).
And if you still can't get enough, be sure to check out the many fabulous results of Christian LawsonPerfect's call for proofinatoot.
That’s it for the beautiful month of May!
Be sure to stop by next month’s Carnival, hosted by Lucy at Cambridge Mathematics. You should submit your favorite blog posts/videos/content from the month of June. If you’d like to host an upcoming show, please get in touch with Katie.
]]>Title: Euclidean Ramsey Theory 2 (of 3).
Lecturer: David Conlon.
Date: November 25, 2016.
Main Topics: Ramsey implies spherical, an algebraic condition for spherical, partition regular equations, an analogous result for edge Ramsey.
Definitions: Spherical, partition regular.
Lecture 1 – Lecture 2 – Lecture 3
Ramsey DocCourse Prague 2016 Index of lectures.
In the first lecture we defined the relevant terms and then established that all (nondegenerate) triangles are Ramsey. In this lecture we will compare the property of being spherical with being Ramsey. In this lecture we will show that Ramsey implies spherical (or more precisely, that non spherical sets cannot be Ramsey).
Definition. A set is spherical if there is an such that .
Typically will be finite, but this is not formally required.
The proofs are those of Erdos et Al, and go by establishing a tight algebraic condition for a set being spherical.
Let where and ; it is a line segment with three points equally spaced.
“The reason is you can take a `spherical shell’ colouring.” These shell colourings are very important.
This doesn’t work for `cube colourings’ (i.e. using a different norm) since by Dvoretsky’s Theorem, hyperplane slices of cubes basically look spherical.
Proof. Fix . Define the colouring by . (You’re taking spherical shells of radii .)
[Picture]
By the Cosine rule we get and . So we get .
Suppose that have the same colour. This means that there is an such that and and , where each .
Putting this into our cosine law info gives
which is a contradiction since the left is but the right is strictly between and .
Eventually we will relate the condition of a set being spherical with a tight algebraic condition. With this in mind, we examine when algebraic conditions can yield Ramsey witnesses. We start with a general discussion of partition regular equations.
For example,
Exercise. If the equation is translation invariant then you get a corresponding density result.
Use this to show that you always get a nontrivial solution.
First an example.
Example. .
We can homogenize this equation by replacing the variables. Use and . This gives the equation .
Basically, these are the only types of partition regular equations.
The number of colours is equal to the number of variables.
This is a strong result of the equation not being partition regular. You can’t have a monochromatic solution, you can’t even have all the paired variables agree!
The idea is to colour whether you are in a certain interval.
Proof. Fix . Colour with if for some integer .
If , then where .
So
Here the first sum is an even number, and the second is , a contradiction.
Now we increase the number of colours to deal with a more general equation.
Proof. Fix . By dividing by it suffices to consider .
Let be the () colouring from Lemma 1.
Define .
Now if , then .
So where .
If this happens for all , then we have a contradiction identical to the one in Lemma 1.
In the original paper there was a similar lemma but it had a worse bound on the number of colours. This improvement was observed by Strauss a little later.
Note that these equations are not susceptible to the “translation trick” since .
The following is the main technical lemma. The proof is purely algebraic.
For readability, we will write instead of . We will make use of the following useful fact:
Proof of . Assume that is spherical and satisfies the first equation. We will show the second equality fails.
Say has centre and radius .
For each we have:
So we must have for each . So by multiplying by and adding up we get
By using the special case of the useful identity, we get:
We know the first sum is by our above calculations, and by assumption we know
a contradiction.
Proof of . Assume is not spherical, and moreover that it is minimal (in the sense that removing any one point makes it spherical). In particular, is not a nondegenerate simplex. So there is a linear relation
Assume that . By minimality, is spherical, and is on a sphere with centre and radius .
Thus
So
here the second sum is , and the first, by minimality, is
which isn’t since the distances of and to are different.
We are now in a position to put everything together.
Proof. Assume is not spherical. So there are constants and a vector such that
and
Technical exercise. Any congruent copy of satisfies the same equations.
(Use the fact that congruence is formed by rotations and translations. The translations will spit out terms like .)
In every nonzero coordinate of use the colouring from Lemma 2, and set . This will give no monochromatic solution to
This is the end of this lecture’s material on pointRamsey. We shift gears a little now.
Instead of colouring points, we can colour pairs of points. This leads to the notion of edge Ramsey. We mention two results in this area.
Proof. Suppose the vertex set is not spherical. Colour the points, using , so that no copy of has a monochromatic vertex set.
Now colour the edge with .
Each edge has the same colour and must contain two distinct vertex colours. So the edge set is bipartite.
This gives us an analogous theorem to the theorem that Ramsey implies spherical.
The proof is a variation on what we’ve seen.
See lecture 1 for references.
]]>When one is ascending a difficult path uphill, it is a good idea to keep your eyes on the path as you move forward. However, it is not a bad idea to stop sometimes, look back, and appreciate the beauty of the ground you have already covered.Continue reading...]]>
This morning I woke up to see that my paper about the Bristol model was announced on arXiv. But unbeknownst to the common arXiv follower, this also marks the end of my thesis. The Hebrew University is kind enough to allow you to just stitch a bunch of your papers (along with an added introduction) and call it a thesis. And by "stitch" I mean literally. If they were published, you're even allowed to use the published .pdf (on the condition that no copyright infringement occurs). Continue reading...
]]>In 1970 G. R. MacLane asked if it is possible for a locally univalent function in the class to have an arc tract, and this question remains open despite several partial results. Here we significantly strengthen these results by introducing new techniques associated with the EremenkoLyubich class for the disc. Also, we adapt a recent powerful technique of C. J. Bishop in order to show that there is a function in the EremenkoLyubich class for the disc that is not in the class .
]]>
Joint work with Ari Meir Brodsky.
Abstract. BenDavid and Shelah proved that if $\lambda$ is a singular stronglimit cardinal and $2^\lambda=\lambda^+$, then $\square^*_\lambda$ entails the existence of a $\lambda$distributive $\lambda^+$Aronszajn tree. Here, it is proved that the same conclusion remains valid after replacing the hypothesis $\square^*_\lambda$ by $\square(\lambda^+,{<\lambda})$.
As $\square(\lambda^+,{<\lambda})$ does not impose a bound on the ordertype of the witnessing clubs, our construction is necessarily different from that of BenDavid and Shelah, and instead uses walks on ordinals augmented with club guessing.
A major component of this work is the study of postprocessing functions and their effect on square sequences. A byproduct of this study is the finding that for $\kappa$ regular uncountable, $\square(\kappa)$ entails the existence of a partition of $\kappa$ into $\kappa$ many fat sets. When contrasted with a classic model of Magidor, this shows that it is equiconsistent with the existence of a weakly compact cardinal that $\omega_2$ cannot be split into two fat sets.
Downloads:
A surprisingly large number of opensource software (OSS) projects is run by volunteers. And I don't mean that "hello world" code you pushed to GitHub (which probably makes up 99% of all OSS repositories), I mean the many successful opensource projects that provide the fertile soil other (small and large) software projects are built on.
In other words, the majority of OSS is run by people privileged enough to spend hours on end to produce something that they then give a way for free. Whether or not OSS developers do it out of conviction, it's often a problem when people end up using privilegebased OSS without realizing it.
The most obvious problem is that privilegebased OSS can essentially go away at any moment. You don't have to look to extreme cases (leftpad, anyone?) to see this happen; projects simply slowly die. You might praise OSS for the fact that anyone can pick up the code and fork it if need be, but in reality dead, privilegebased OSS is more like an unfinished construction site; it's easier to start from scratch and thus the cycle repeats.
However, this is so obvious, it's not really a problem, I think. In any case it's not what I mean.
There's a lot to be said in favor of developing OSS out of conviction. It frequently helps people and adds diversity to the ecosystem. The trouble is that privilegebased OSS can be highly toxic.
One toxic variant is "Silicon Valley style OSS" where developers do not act out of conviction but more out of necessity to get ahead in a questionable job market ("GitHub is your resume"kindofthing). If your hipster company hires people only due to their volunteer OSS credentials, then you are effectively hiring them by their privilege, creating a toxic environment and reducing diversity.
Reversely, you have the toxicity of people relying on OSS software not being willing to contribute to the development of OSS because privileged people make it work. Just the other day I was talking with a potential client who described how they use pandoc in production. If you do this at scale, then you're basing the integrity of your production workflow on how much John MacFarlane could procrastinate over the years.
For OSS developer, this can turn into a toxic reality because users often think they deserve access to the developer's privilege. That is, they can become highly aggressive when they find a bug in the OSS software they're using, especially when it impacts them. This gets extreme when we're talking about companies and use of privilegebased OSS in production. Company employees quickly try to exert pressure on OSS projects to fix things  yet refuse to actually contribute to development any which way or even acknowledging the work that went into a piece of software that they themselves chose to build upon.
Obviously, there are other ways of doing OSS software development. There's transparencydriven OSS (e.g., security related tools, browsers), there's sharedburden OSS (e.g., joining forces to lower costs), there's donationbased, crowdsourced, and bountydriven OSS and many others  Nadia Eghbal lists a few in her lemonadestand on GitHub. Also ask about governance models.
Long story short, if you're using opensource software, especially in a professional context, make sure to check what model it's based on. Also, don't be toxic.
These thoughts were far from original.
This is where I have an issue with the "hire people for their side projects" mentality.
— Stewart ScottCurran (@stewartsc) May 25 2016
Wider scope
Overall, the mathematical community does not value open source mathematical software in proportion to its value, and doesn't understand its importance to mathematical research and education. I would like to say that things have got a lot better over the last decade, but I don't think they have. My personal experience is that much of the "next generation" of mathematicians who would have changed how the math community approaches open source software are now in industry, or soon will be, and hence they have no impact on academic mathematical culture. Every one of my Ph.D. students are now at Google/Facebook/etc.
Organisations in “the open space” are often community driven. Groups come together to solve a problem, and in a few cases they succeed. Most fail, and most fail pretty early. Those that survive the initial phase often experience massive growth, sometimes beyond the wildest dreams of those who started them. This brings some challenges.
Sustainability is a big one: too many of these organisations lurch from grant to grant, depending on the largesse of philanthropists or government funders. Most of these eventually fail or stagnate. Some negotiate this transition by turning private and obtaining VC or Angel funds. Eventually most of these are sold off to incumbent players, and gradually lose the central thread of openness and just becoming part of the service background in their space. Nothing wrong with that but they’re no longer really part of the open community at the end of this process.
But some organisations succeed and find a model: donations, memberships, advertising, fee for service have all been successful in different spaces. These can grow to be sizeable companies, ones that need professional staff and business discipline to manage complex operations, significant infrastructures, and substantial financial flows and reporting. No multimillion dollar a year organisation is going to run for very long on volunteer labour, at least not where those volunteers need to work for a living.
Passion can also be a problem, as well as being a driver. Without that passion and without that community nothing gets done. Indeed without the passion many notforprofit organisations wouldn’t be able to attract staff at the rates that they can reasonably pay. The community is a core asset.
Still, there's now a small but clear core within the CG together with a useful group of "lurkers". I think this year we're entering the productive stage for this community group.
The dominant interest of the core group (i.e., the people actually doing work) is accessibility. What surprised me somewhat was that the core group seems to be in agreement that MathML is not suitable for accessibility, not just because it is effectively deprecated on the web but also because of its inherent limitations. (If you care for nuance and read on, this doesn't mean MathML isn't a decent intermediary for creating accessible web content.)
My own focus has been on "deep labels" which will now tie nicely into our work at MathJax for our recent grant from the Simons Foundation. The idea is quite simple, really.
Thus I've been building and testing demos that work with what we've got  HTML and SVG enriched via ARIA.
While I'm currently building manual prototypes, obviously one eye is on our work on the speechruleengine, i.e., keeping automation of the process in mind. Similarly, I've been trying to think about potential improvements to standards that might give us much larger improvements / simplifications (but that's for another post).
At the same time, while automated analysis of content will only improve, I think manual overrides will continue to be critical. Whether it's to fix a poor result from the heuristics or whether it is to customize content (e.g., to match author preferences).
Obviously, I didn't want to enrich the output but the input. Given that these demos work with MathJax, the natural starting point is MathML (since that's MathJax's internal format). But MathML isn't really special or better than any other format; whatever input format your favorite tool uses, the same methods should be applicable (though some things will undoubtedly be harder/easier to do in other formats).
MathML in itself lacks the means to provide meaningful information to the accessibility tree; at most, it can present (pretty vague) layout information, combined with some misleading information on semantics (e.g., thinking that <mfrac>
always indicates some kind of fraction). But MathML has the benefit of being XML so we can easily add ARIA attributes without running into practical issues.
Here's a very simple but typical example: a common notation for the derivative of a function is a dot above it. In MathML, this is usually realized as an <mover>
.
<math>
<mover>
<mi>x</mi>
<mo>˙<! ˙ ></mo>
</mover>
</math>
You might be tempted to think that the "real" solution would be some kind of semantic markup (e.g., using <diff>
) but in the real world, the content is what it is and you want to enhance it.
Now even the simplest MathML accessibility tool should have the sense to voice the Unicode content ("x, dot above") but it might also try to convey the layout information of an mover
("x with dot over it"). But it shouldn't try anything beyond that because the markup does not provide more information than that. In reality, those few tools with decent heuristics will easily cause issues, e.g., any superscripted 2 is read as "squared".
Unfortunately, a dot above can mean other things besides "derivative of", depending on the context and content  if you ever run into a dot above an equal sign or a digit you'll probably guess that the dot does not represent the concept of a derivative of (then again someone probably used it that way so have fun figuring that one out).
So it's a mess.
Let's use what ARIA has given us to make it less of a mess: a simple and efficient means of providing meaningful textual alternatives for visual presentation:
<math>
<mover arialabel="derivative of x">
<mi>x</mi>
<mo>˙<! ˙ ></mo>
</mover>
</math>
This is obviously a very simple example. The most immediate questions are probably:
I believe the answer to both is yes.
The main demo I built is work in progress. It is available on Codepen and I recently started versioning it as a gist.
The demo covers several examples that hopefully already cover many common situations and I'll continue to work on them.
A lot of tweaking happened once I started to test this in screenreaders in earnest.
One of the first problems I ran into is what James Teh described in WoeARIA: it's not always clear what AT should expose when we muck about by arialabeling things like this.
Inevitably, I also needed a common accessibility hack, "offscreen" rendering of content. As a simple but extremely important example, you need this when facing the fact that, in MathML's <mfrac>
the fraction bar is only implicit and thus lacks an node we could attach a label to (arguably the biggest WTF collision between traditional math rendering aka print and web markup).
I currently favor a somewhat convoluted solution:
<mrow arialabel="screenreader only"><mpadded width="1em"><mphantom><mtext>M</mtext></mphantom></mpadded></mrow>
The main advantage is backward compatibility and reusability because this should render in any MathML renderer without (many) sideeffects. It also (in part) gets us around the "ARIAwoe" or the fact that an empty <span>
with arialabel
should be ignored.
So far I've tested NVDA, JAWS, VoiceOver, Orca, and ChromeVox in several browsers. Some recordings are already available in a dedicate playlist on MathJax's YouTube channel. Since I didn't want to add commentary, they are a bit difficult to follow so the summary below should be helpful.
arialabel
s completelyOSX El Capitan
Orca 3.20, Ubuntu 16.10
JAWS 17, Windows 7
ChromeVox v53
As you can see, the results are mixed. For each combination of AT+browser+OS, there's some combination that works roughly as expected but that's about it. SVG seems a clear winner despite VO's reluctance; I need to exploretitle
/desc
a bit further (which has different support levels).
Still, I think the situation is already better than what MathML can give you today, in particular because the few significant issues are nothing particular to MathML or math, they're just annoying SVG or HTML accessibility issues, many of which can be easily fixed (as opposed to implementing good math support based on MathML). The fact that MathML accessiblity tools fail to support arialabels is not surprising, of course, and a typical example of how MathML support (as little as it is) continues to fall further and further behind HTML and SVG. And that's a good thing.
Now some might see this "fixed" enrichment as a step back compared to MathJax's Accessibility Extensions (using speechruleengine on the client) because the extensions can provide numerous speech rules and verbosity settings as well as summary information. I would disagree. I've never been a fan of varying speech rules (just like I wouldn't be a fan of AT rearranging a sentence). Also, speech rules mostly differ by newer ones being more refined than older ones.
Verbosity is simply a general accessibility problem and it should be dealt with in generality (as it already is, e.g., for punctuation). Summary information is a great problem but really a limitation of current web technology and something that's just as needed for infographics or data visualization as it is for mathematics. We do not need isolated solutions here either.
Simple: more testing.
On the one hand, testing more AT combinations and evaluating other approaches. On the other hand, creating more and complex samples.
Others on the MathOnWeb CG have tried different approaches and so we will also work on getting feedback from the accessibility community in general, in particular figuring out how improved standards might help us.
For me personally, the goal is to develop a strategy for next year's work at MathJax where we want the speechruleengine to add deep labels directly. I think that would solve the last major piece of the puzzle for math on the web in its current form. Then we can finally leave the legacy approaches with isolated standards and tools behind to focus on moving the web forward as a whole.
]]>Theorem. Suppose that \(\kappa\) is regular and uncountable, and \(\pi\colon\kappa\to\kappa\) is a bijection mapping stationary sets to stationary sets. Then there is a club \(C\subseteq\kappa\) such that \(\pi\restriction C=\operatorname{id}\). Continue reading...
]]>I was reminded of this old note yesterday. This snippet goes back to JMM 2016 when I had coffee with Izabella Łaba. Of course, Izabella is one of my favorite bloggers (starting all the way back when procrastination made us launch mathblogging.org  shout out to Felix, Fred, and Sam!) but she is also a kickass researcher who amongst the many great things she does happens to sit on the editorial board of the (then newly fandangled) arXiv overlay journal Discrete Analysis otherwise known as "that Tim Gowers journal thing".
Discrete Analysis is probably the most relevant arXiv overlay journal in mathematics (ok, I admit I didn't search around much for other noteworthy ones) and the gut reaction when it comes to arXiv overlay journals (and Discrete Analysis in particular) seems to be: "What if it fails?". But like jumping in the Matrix, failure really wouldn't mean anything.
Instead, I've been wondering more about "What if it succeeds?". Of course that's because I expect it to succeed but in either way I don't think people think a lot about that. Arguably, I'm not awfully qualified but then again anyone can go through Kent Anderson's list of 96 things Publishers Do. Most of these, I'm guessing, you don't care about as an arXiv overlay journal so perhaps Cameron Neylon's shorter list is more on point. Ultimately, I think, it is simple: what does a journal need to succeed? Highquality papers.
Quality comes in many forms but basically there are two areas: scientific quality and production quality. Scientific quality includes, at least, attracting papers the community will approve of, attracting authors that impress the community, and an editorial board that can spot the former and attract the latter. Of course, those are not at all separate but papers make journals influential, journals make authors influential etc pp. (And no, merit does not come into play, don't be silly.) I can't really judge it (not being a research mathematician anymore, let alone a discrete analysis person) but the editorial board looks to be full of influential, highprofile people and the first paper was Terry Tao's solution to Erdős's discrepancy problem; so it seems likely that part will work.
Production quality includes, at least, typography, copyediting, archiving, and marketing. Discrete Analaysis can probably make that work as well as they care because, as Gowers pointed out, they expect they won't have to. That might seem arrogant to anyone with even a bit of knowledge from the trenches of academic publishing, but I think they're probably right in expecting they won't have to. I admit that is in part speculation, but I would expect that a high profile math journal can probably expect both their authors to have spent more time on their manuscript (more presubmission review from peers, more iterations from themselves as the result is "big" etc) and they can probably expect their editors to work harder (they actually give a damn about the paper they read b/c the result is interesting, they have themselves higher expectations thus provide more detailed reports, they have simply more experience and relevant skills etc). And marketing, well, it's that Gowers journal thing, remember?
So this all looks great. Got the goods, can compete.
Except there are a few things that I think are terrible flaws; in no way fatal flaws (quite possibly the opposite) but ones with negative side effects that worry me.
To start with, overlay journals do the silly extreme libertarian thing of pretending the infrastructure they use doesn't cost anything. Even if the costs of the current technology might be very small, overlay journals will have to stick to the cheapest available tech, ignoring (let alone helping) the transformation of scientific communication.
A more important problem is: can this scale? I don't think it can (not much anyway). Research quality obviously doesn't scale well  if everyone is a top journal, nobody is. Regarding production quality in "lesser" journals, I don't think authors will invest much in their manuscripts and reviewers will be less likely to have the skills or invest extra time. It still might work if journals started to rely on a more iterative process where postpublication feedback leads to revisions. (I mean, traditionally published journal articles can be awful piles of unedited crap, why expect more from an overlay journal, amiright?) But on the one hand, the community would have to accept that, i.e., it would require a much more significant change in scientific culture, and on the other hand people would have to, well, read papers and give feedback  where the average number of readers for a math research paper is probably less than 1. Seems unlikely. So we might get elite journals that can get away with this model commercially but anyone else is screwed; not a fan.
The third problem I see is more severe as it relates to the structure of scientific communities: who watches the watchers? Years ago I wrote that my biggest problem with academic communities (and the greatest strength of its publishing system) lies in its power structure: the key to power lies with editorial boards which are predominantly aristocratic. Societydriven journals actually have democratic oversight for their editorial boards (as mild as its effect might be) and even commercial publishers have shareholder oversight, as "unscientific" as their interest may be. But overlay journals have nobody watching them. You might argue the free market will take care of it but it might just be that journals are clubs and that scholarly communication is more like general taxation.
And that combination worries me. The unique ability of elite overlay journals to succeed commercially (as in: providing a valuable product) combined with a lack of checks and balances might lead to an imbalance that cannot be corrected.
But what do I know. Maybe such journals will realize the risk associated with their success and take responsibility for their actions and their effect on the community at large. And then maye they will focus on innovation and on reproducibility of their model for average ("mediocre") journals that the majority of researchers publish in. I've seen crazier things.
]]>So the next order of business is finding a position for next year. So far nothing came up. But I'm open to hearing from the few readers of my blog if they know about something, or have some offers that might be suitable for me. Continue reading...
]]>Registration for the 2017 Southwestern Undergraduate Mathematics Research Conference (aka SUnMaRC) is now open! Northern Arizona University is hosting this year’s conference on March 31April 2, 2017. We are excited to announce Kathryn Bryant (Colorado College), Henry Segerman (Oklahoma State University), and Steve Wilson (NAU, emeritus) as our invited speakers.
The goal of the conference is to welcome undergraduates to the wonderful world of mathematics research, to develop and foster a rich social network between the mathematics students and faculty throughout the great Southwest, and to celebrate the accomplishments of our undergraduate students. We encourage undergraduate students from all years of study to participate and give presentations in any area of mathematics, including applications to other disciplines. However, while we do recommend giving a talk, it is not a requirement for conference participation. To register for the conference and to submit a title and abstract for a student presentation, visit the 2017 SunMaRC Registration page.
The conference began in 2004 as the Arizona Mathematics Undergraduate Conference. In 2008, the conference changed to SUnMaRC to recognize the participation of institutions throughout the southwest.
If you have any questions about this year’s SUnMaRC, please contact one of the conference organizers:
]]>Matti was a kind teacher, even if sometimes overpedantic. Continue reading...
]]>One of my former students, Andrew Lebovitz, recently posted a link on Facebook to a Nature article that summarizes a paper, titled The classical origin of modern mathematics, which completed a comprehensive analysis of the MGP database. One of the interesting findings was that the individuals in the database fall into 84 distinct family trees with twothirds of the world’s mathematicians concentrated in just 24 of them.
After reading the Nature article, I was motivated to see if I could figure out whether I belonged to one of the 24 families. It wasn’t obvious to me how I would do this without manually clicking on my advisor (Richard M. Green), then my advisor’s advisor, etc. This was slightly more complicated than I expected because there were quite a few ancestors with 2 advisors, so I had to navigate down multiple paths. As I clicked around, I drew out my family tree in a notebook.
Here is what I discovered. My longest branch goes back to Nicolo Fontana Tartaglia (currently 14,428 descendants). My tree includes Isaac Newton, Galileo Galilei, and Marin Mersenne (who Mersenne primes were named after). Interestingly, no one on this path belongs to one of the 24 families mentioned in The classical origin of modern mathematics. Also, I was disappointed to find out that I wasn’t related to Leonhard Euler. However, I am a descendant of Henry Bracken, who is the head of one of the 24 families.
I posted some of this information on Facebook and asked if anyone knew how to automatically create a nice visualization of the directed graph corresponding to my family tree. Chris Drupieski replied and pointed out a program called Geneagrapher, which was built to do exactly what I was looking for. In particular, Geneagrapher gathers information for building math genealogy trees from the MGP, which is then stored in dot file format. This data can then be passed to Graphviz to generate a directed graph.
Here are the steps that I completed to get Geneagrapher up and running on my computer running MacOS 10.11. The Geneagrapher website suggests using easy_install
via Terminal, but this didn’t immediately work for me. It often seems that doing anything with Python on my Mac requires a few extra steps. After doing a little searching around, I found a post on Stack Overflow that solved my issue. At the command line, I typed the following:
sudo chown R <your_user>:wheel /Library/Python/2.7/sitepackages/
Of course, you should replace <your_user>
with your username. Note that using sudo
requires you to enter your password. Next, I installed Geneagrapher using the following:
easy_install http://www.davidalber.net/dist/geneagrapher/Geneagrapher0.2.1r2.tar.gz
In order to use Geneagrapher, you need to input a record number from MGP. Mine is 125763. At the command line, I typed:
ggrapher f ernst.dot a 125763
You can replace ernst
with whatever you’d like the output file to be called. The next step is to pass the dot file to Graphviz. If you don’t already have Graphviz installed, you can do so using Homebrew (which is also easy to install):
brew install graphviz
Following the Geneagrapher instructions, I typed the following to generate my family tree:
dot Tpng ernst.dot > ernst.png
Maybe it is worth mentioning that unless you specify otherwise, the dot and png files will be stored in your home directory. Below is my mathematical family tree created using Geneagrapher. As you can see, it took a while for my ancestors to leave the University of Cambridge.
]]>Nonmathematicians often tend to be Platonists "by default", so they will assume that every question has an answer and sometimes it's just that we don't know that answer. But it's out there. It's a fine approach, but it can somewhat fly in the face of independence if you are not trained to think about the difference between true and provable. Continue reading...
]]>Title: Dual Ramsey, the Gurarij space and the Poulsen simplex 1 (of 3).
Lecturer: Dana Bartošová.
Date: December 12, 2016.
Main Topics: Comparison of various Fraïssé settings, metric Fraïssé definitions and properties, KPT of metric structures, Thick sets
Definitions: continuous logic, metric Fraïssé properties, NAP (near amalgamation property), PP (Polish Property), ARP (Approximate Ramsey Property), Thick, Thick partition regular.
Lecture 1 – Lecture 2 – Lecture 3
Ramsey DocCourse Prague 2016 Index of lectures.
Throughout the DocCourse we have primarily focused on Fraïssé limits of finite structures. As we saw in Solecki’s first lecture (not posted yet), it makes sense, and is useful, to consider Fraïssé limits in a broader context. Today we will discuss those other contexts.
Solecki’s first lecture discussed how to take projective Fraïssé limits. Panagiotopolous’ lecture (not posted yet) looked at a specific application of these projective limits. We will see how to take metric (direct) Fraïssé limits.
Discrete  Compact  Metric Structure  

Size  Countable  Separable  Separable, complete 
Limit  Fraïssé limit  Quotient of the projective limit  (direct or projective) Metric Fraïssé limit 
Homogeneity  (ultra)homogeneity  Projective approximate homogeneity  Approximate homogeneity (*) 
Automorphism group  nonarchimedian groups (closed subgroups of  homeomorphism groups  Polish Groups 
KPT, extremely amenable iff  RP  Dual Ramsey  Approximate RP (**) 
Metrizability of UMF iff  finite Ramsey degree  (***)  (Open) Compact RP? 
Where we’ve seen these  Classical  Solecki’s lectures  These lectures 
(*) – Exact homogeneity is often not possible.
(**) – In the projective setting this is fairly unexplored. These proofs are usually via direct (discrete) Ramsey, or through concentration of measure.
(***) – You have KPT before you take the quotient, but lose it after taking the quotient. e.g. UMF(prepseudo arc) is not metrizable (through RP). A question of Uspenskij asks about the UMF(pseudo arc).
In the context of Banach spaces, it makes sense to use continuous logic. This is where we instead of the usual valued logic we allow sentences to take on values in the interval . We also suitably adjust the logical constructives.
Classical logic  Continuous logic 

True  0 
False  1 
Now we define functions and relations. Let be a complete metric space. So will be given the sup metric.
Then functions and relations must satisfy the usual things that functions and relations satisfy in classical logic.
Finitely generated substructures  Limit  maps  Language  

Separable metric spaces  finite metric spaces  Separable Urysohn space  isometric embedding  just the distance 
Separable Banach spaces  finite dimensional Banach spaces (**)  Gurarij space  isometric linear embedding  
Separable Choquet spaces  finite dimensional simplices  Poulsen simplex  affine homeomorphisms (*)  Something that captures the convex structure 
(*) – An affine homeomorphism sends and sends extreme points to extreme points, then is extended affinely to the rest of the simplex. The metric here is not canonical.
(**) – Similar to the discrete case, to take a limit you only need a cofinal sequence. In this case we take .
In continuous logic the maps between models are isometric embeddings that preserves functions and relations.
In the classical Fraïssé setting we looked at homogeneity, HP, JEP and AP. These notions have suitable generalizations in the metric Fraïssé setting.
We say that is approximately ultrahomogeneous (AUH) if and for every morphism, and for all , there is a such that .
is the collection of finitely generated substructures of .
We now explain NAP and PP. The NAP is a striaghtforward generalization of AP.
such that
The PP measures how closely you can embed two metric spaces.
We say satisfies the Polish Property (PP) if is separable for all .
This gives us the following Fraïssé theorem for metric structures.
Recall that is the separable Urysohn space. It is the (unique) complete, separable metric space, universal for separable metric spaces and (exactly) ultrahomogeneous with respect to finite metric spaces.
Its age is the collection of finite metric spaces. It is a metric Fraïssé class.
Its automorphism group has a similar universal property.
See these notes for more information.
Recall the following fact about (classical) Fraïssé structures.
The following observation of Melleray is the corresponding fact for metric structures. It has a similar proof to the classical fact.
For every orbit closure in of a point add a relational symbol called .
The first relevant result is the following:
This proof uses the finite Ramsey theorem and concentration of measure.
The KPT theorem for metric structures is given by the following.
We define the approximate Ramsey Property.
(ARP):
there is a such that
such that
Here , and the fattening is using the embedding distance (which we haven't defined).
Recall that in the infinite case, rigidity was needed to have the embedding RP. That is why in finite metric spaces we added linear orders to get the RP. However, metric spaces do satisfy the ARP (by Pestov from extreme amenabilty of , without needing to add linear orders.
Also, by using the usual compactness arguments, we can assume that the witness to ARP is the full Fraïssé limit.
In the KPT correspondence, we saw a useful connection between the stabilizer of a set and collections of finite structures. See Lionel Ngyuen van The’s first DocCourse lecture.
Here we mention an analogous connection.
So we can reword the ARP for finite metric spaces, by transfering the colouring to a colouring .
Thickness is a group property that captures some Ramsey properties. This is desirable because we would like to be able to detect Ramsey type phenomena from the group itself, without having to know the underlying Fraïssé limit.
is thick partition regular iff there is a that is thick.
This is really just unwinding definitions. Then by general topological dynamics abstract nonsense we get:
Note that this is a theorem just about groups. This doesn’t use much of the structure of . Our goal is to prove extreme amenability without having to first prove Ramsey theorems.
In the next lectures we will examine the Gurarij space and prove the ARP for (i.e. Banach spaces).
(This is incomplete – Mike)
Title: Bootcamp 1 – Informal meeting.
Lecturer: Jaroslav Nešetřil.
Date: September 20, 2016.
Main Topics: Overview over the topics of the DocCourse; classical result in Ramsey theory
Definitions: Arrow notation, Ramsey numbers, arithmetical progression
Bootcamp 1 – Bootcamp 2 – Bootcamp 3 – Bootcamp 4 – Bootcamp 5 – Bootcamp 6 – Bootcamp 7 – Bootcamp 8
The main scope of this lecture was to give a historical overview over classical results in Ramsey theory, including Ramsey’s theorem itself. Further the program of the DocCourse was presented, which can be found here.
The three books below are a main references for Ramsey theory in general and the Bootcamp lectures in particular. Jarik also passed around an original version of Ramsey’s paper, which is depicted on the conference poster.
In order to phrase Ramsey’s theorems we first introduce some standard notation:
Then Ramsey’s theorem states as follows:
A proof of Ramsey’s theorem can be found in the notes to David Fox’ lectures (Mike: Coming soon!), including some estimates for the corresponding Ramsey numbers:
By the pigeonhole principle we have . However already the situation for Ramsey number is much more complex, only estimates are known for .
Ramsey’s work did not result from pure interest in combinatorics, but was motivated by Hilbert’s Entscheidungsproblem, the problem of finding an algorithm that tells if every statement expressible in firstorder logic is provable (from a given set of axioms). The finite Ramsey theorem was only used as an auxiliary result in “On a Problem of Formal Logic.”, in order to prove that every formula of the form
is decidable.
We remark that by Gödel’s incompleteness Theorem, the Entscheidungsproblem in general is not decidable; by a result of Trakthenbrot already adding one additional quantifier alternation results in undecidable formulas.
In the same paper Ramsey also presented a proof for the following infinite version of his theorem:
The proof of the infinite Ramsey theorem requires the axiom of choice. There exists a slight strengthening of the Finite Ramsey theorem, which we will denote by FRT*. In FRT*, we additionally can assume that the minimum monochromatic set is bounded by the size of :
We are going to show that the infinite Ramsey theorem implies the strengthened version of the finite Ramsey theorem:
Note that, since the above proof of the FRT* uses the infinite Ramsey theorem, it requires also the axiom of choice. It can be shown that this assumption is indeed necessary: Paris and Harrington proved that FRT* is a true statement about the integers that could be stated in the language of arithmetic, but not proved in Peano arithmetic. It was already known that such statements existed by Gödel’s first incompleteness theorem, however no examples of “natural” such theorems were known.
Their proof lead also to the notion of indiscernibles in mathematical logic, i.e. are objects which cannot be distinguished by any property or relation defined by a formula.
As mentioned above, Ramsey himself used his result only as an auxiliary result to prove statements about decidability. The Happy ending theorem is often considered as starting point for the development of Ramsey theory as a whole new branch of mathematics:
Ramsey’s theorem was preceded by several other results, which we nowadays consider to be part of Ramsey theory, although they were also not studied from a combinatorial point of view, when they were first proven. One example is Van der Waerden’s theorem:
In reproving a theorem of Dickson on a modular version of Fermat’s conjecture, Schur showed the following:
Hilbert’s cube lemma is probably the earliest result which can be viewed as a Ramseytype theorem (besides, of course, the pigeonhole principle). It was established in connection with investigations on the irreducibility of rational functions with integer coefficients.
Title: Bootcamp 2 (of 8)
Lecturer: Jaroslav Nešetřil.
Date: September 21, 2016.
Main Topics: The Rado graph, homogeneous structures, universal graphs
Definitions: Language, structures, homomorphisms, embeddings, homogeneity, universality, Rado graph (Random graph),…
Bootcamp 1 – Bootcamp 2 – Bootcamp 3 – Bootcamp 4 – Bootcamp 5 – Bootcamp 6 – Bootcamp 7 – Bootcamp 8
In this lecture we discussed some standard notions from model theory that will be used in the rest of the Bootcamp lectures. Further we discussed the Rado graph (also known as Random graph) as an example of a homogeneous structure.
Then an structure is a triple , where is called the domain of and the interpretation function. For we require that for every relational symbol (i.e. is an ary relation on ) and is a function from A$.
For simplicity, we usually don’t talk about the interpretation function and write and . If it is clear from the context, we sometimes abuse notation and write for both the symbol and its interpretation in a structure.
Constants can be regarded as unary singleton relations, or as 0ary functions. However, in the Bootcamp lectures, we are only going to discuss relational structures, i.e. structures whose language only consists of relational symbols.
Injective homomorphisms are called monomorphisms, injective strong homomorphisms are called embeddings, bijective embeddings are called isomorphisms. An isomorphism from a structure to itself is called an automorphism of .
We say is a substructure , if and the identity is an embedding of into . If there is an embedding of , we call the image a copy of in .
Erdös and Rényi showed the paradoxical result that there is a unique (and highly symmetric) countably infinite random graph. We are going to discuss this graph and some of its properties in this section.
Suppose we have already constructed an isomorphism from a finite subset to . Then let be the first element of ; it gives us a partition of into the set of its neighbors and nonneighbors . By the extension property of , there is also a vertex in such that has an edge with all elements of and has no edge with elements of . By setting we extended the given isomorphism to .
To ensure that every vertex of is in the image of we alternate in the next step, finding a suitable preimage of the first element of . This can be done symmetrically by the extension property of .
Since both graphs and are countable, the union of this ascending sequence of finite isomorphisms is an isomorphism from to .
The technique used in proof above is known as backandforth argument or zigzag argument. This proof techniques appears also in other talks of the course, in particular in the proof of Fraïssé’s theorem in Bootcamp 5.
It is not difficult to show that there are graphs with the extension property. An explicit description of such a graph was given by Rado in 1964. The vertex set of the Rado graph are the natural numbers, where for there is an edge between and if and only if the binary representation of has a on its th position.
There is also a probabilistic characterization of such graphs by Erdös and Rényi, which preceded Rado’s construction. Let us denote by a random graph a probabilistic distribution over graphs, in which the probabilities for edges are distributed independently, with probability each (Note by Michael: In literature the term “random graph” sometimes also refers to graphs generated by some other random process).
Then the following holds:
By the above theorem the Rado graph is often also called the Random graph. The Rado graph has several other nice features, making it a highly symmetric structure:
Examples:
In the case of graphs a full classification of the homogeneous graphs is known: in the finite case this classification is due to Gardiner, in the countable case due to Lachlan and Woodrow.
We will hear more about homogeneous structures and a way of constructing them in Bootcamp 5.
Examples:
In this section we are going to show that not for every class of countable structure there is a universal structure. A counterexample for graphs was given by Füredi and Komjáth:
We remark that this result was proven in a more general setting (substitute by any finite, 2connected, but not complete graph); but here we only present a proof for .
(Michael: My notes on the proof of this lemma are not complete…)
Now let us take the hypergraph given by the above Lemma. Further let , be graphs on 7element vertex set, such that in the first 4 elements form a path and the last 3 a cycle; and in also the last 3 elements form a cycle and there is an edge from the first to the forth vertex.
For every function we then form a free graph on , by replacing every hyperedge in by if and by if . Note that the graph is welldefined and free by the properties of .
Now assume that there is a countable universal free graph . Then has to embed all the graphs of the form ; For every let be an embedding of into . Since is countable, there are two graphs , , such that and agree on the set . But since , there has to be a minimal integer , where they disagree. Then, by construction of the graphs and , the union has to contain a 4cycle. But this is a contradiction.
Yesterday, however, I spent most of my day thinking about how weas a collective of set theoriststeach axiomatic set theory. About that usual course: axioms, ordinals, induction, wellfounded sets, reflection, \(V=L\) and the consistency of \(\GCH\) and \(\AC\), some basic combinatorics (clubs, Fodor's lemma, maybe Solovay or even Silver's theorem). Up to some rudimentary permutation. Continue reading...
]]>I’ve been really enjoying my new job at Time Service in Toledo. I’m about to finish my third month here, and I expect I’ll be staying with this job for quite a while. I find that working in business gives me a variety of interesting problems to solve, and although they’re not deep and abstract in the same way as math research problems, they still require a lot of creative thinking and give me challenges to work on over time and puzzles to chew on as I drift off to sleep, in my morning shower, etc., just like math research did. The whole operation of helping to run a business feels like a big optimization problem — how do I figure out the best way to use all of our company’s resources to the greatest effect?
I hope all my friends in the New York Logic community are doing well. Please keep in touch!
]]>I was very happy when the professor, Matania BenArtzi, allowed me to write a final paper about the usage of the axiom of choice in the course, instead of taking an exam. Continue reading...
]]>Below are 15 problems from the course. Originally I was only going to list 5, but it was hard enough to only pick 15. I attempted to showcase a variety of problems that utilize different ways of thinking. I’m intentionally not providing any solutions. Some of these problems are classics or variations on classics. Have fun playing!
If you want to see more problems from the course, go here.
Note: The #loveyourmath 5day campaign is sponsored by the Mathematical Association of America. The goal of the campaign is to engage a general audience across a broad representation of mathematics, whether it is biology, patterns, textbooks, art, or puzzles.
]]>It turns out that up to isomorphism, there are exactly 5 groups of order 8. Below are representatives from each isomorphism class:
The first three groups listed above are abelian while the last two are not. It’s a fairly straightforward exercise to prove that none of these groups are isomorphic to each other. It’s a bit more work to prove that the list is complete. The Fundamental Theorem of Finitely Generated Abelian Groups guarantees that we haven’t omitted any abelian groups of order 8. Handling the nonabelian case is trickier. If you want to know more about to prove that the classification above is correct, check out the Mathematics Stack Exchange post here, the GroupProps wiki page about groups of order 8, and the nice classification of all groups of order less or equal to 8 that is located here.
Since groups have binary operations at their core, we can represent a finite group using a table, called a group table. In order to help out minds recognize patterns in the table, we can color the entries in the table according to which group element occurs. Of course, if we rearrange the column and row headings of the table, we have to rearrange or recolor the entries of the table accordingly. Doing so may make some patterns more or less visually recognizable. Similar to the book Visual Group Theory by Nathan Carter (Bentley University), I utilize colored group tables in several chapters of An InquiryBased Approach to Abstract Algebra, which is an opensource abstract algebra book that I wrote to be used with an IBL approach to the subject.
While I was teaching out of Carter’s book during the summer of 2009, one of my students (Michelle Reagan) made five quilts that correspond to colored group tables for the five groups of order 8. Here are pictures of the quilts.
It’s a fun exercise to figure out which quilt corresponds to which group. I’ll leave it to you to think about.
Note: The #loveyourmath 5day campaign is sponsored by the Mathematical Association of America. The goal of the campaign is to engage a general audience across a broad representation of mathematics, whether it is biology, patterns, textbooks, art, or puzzles.
]]>This text presents the Eulerian numbers in the context of modern enumerative, algebraic, and geometric combinatorics. The book first studies Eulerian numbers from a purely combinatorial point of view, then embarks on a tour of how these numbers arise in the study of hyperplane arrangements, polytopes, and simplicial complexes. Some topics include a thorough discussion of gammanonnegativity and realrootedness for Eulerian polynomials, as well as the weak order and the shard intersection order of the symmetric group.
The book also includes a parallel story of Catalan combinatorics, wherein the Eulerian numbers are replaced with Narayana numbers. Again there is a progression from combinatorics to geometry, including discussion of the associahedron and the lattice of noncrossing partitions.
The final chapters discuss how both the Eulerian and Narayana numbers have analogues in any finite Coxeter group, with many of the same enumerative and geometric properties. There are four supplemental chapters throughout, which survey more advanced topics, including some open problems in combinatorial topology.
This textbook will serve a resource for experts in the field as well as for graduate students and others hoping to learn about these topics for the first time.
Generally speaking, most of my research in pure mathematics falls in the category of algebraic combinatorics. However, I’ve had very little formal training in combinatorics. It turns out that I know quite a bit about Catalan combinatorics, but again, it’s not a subject that I’ve explicitly studied. Prior to opening the book, I knew next to nothing about Eulerian numbers, let alone Narayana numbers.
Right around the time I found out I would be teaching our graduate combinatorics class during the Fall 2016 semester, I learned about Kyle’s book. I was really looking forward to teaching the class because I figured that one of the best ways to fill in my lack of formal training in combinatorics was to teach a class about it. After thumbing through Kyle’s book (and thinking, “wow, I don’t really know any of this stuff!”), I decided that I could run the class as a sort of “topics course” focusing on Eulerian numbers and Catalan combinatorics while hitting many of the core ideas of enumerative combinatorics along the way. As a bonus, I would be forced to learn lots of cool things that relate to my research interests, many of which I probably should have know more about anyway.
I’m currently in week 5 of my Topics in Combinatorics graduate course in which we are closely following Kyle’s book. Despite the fact that we’ve barely covered two chapters, I’m absolutely in love with the book and the content. It’s so much fun! I have to admit that I don’t always know which specific topics are key ideas and which are just fun side stories, but I think that’s mostly true every time one teaches a course for the first time. One of the things I really like about the themes in the book is that connects with cutting edge research topics. We’re learning about “current events” in algebraic/enumerative combinatorics.
My only minor complaint is that I wish Kyle provided less detail in the hints/solutions for the exercises in the back of the book. On the other hand, there have been a couple times where I’ve thought, “geez, there’s no way I would have ever come up with that argument without significant guidance.”
Note: The #loveyourmath 5day campaign is sponsored by the Mathematical Association of America. The goal of the campaign is to engage a general audience across a broad representation of mathematics, whether it is biology, patterns, textbooks, art, or puzzles.
]]>As a side project, I hope to find some time to do a bit of research for MIRI. I’ve discussed MIRI research in a couple of recent posts here. I plan to continue updating this blog with stuff on MIRI research and other updates on my life. I’ll miss my colleagues in New York, and I hope we keep in touch. My students are welcome to keep in touch as well.
]]>Quantilization is a form of mild optimization where you tell an AI to choose something at random from (for instance) the top 10% of best solutions, rather than taking the best solution. This helps to get around the problem of an agent whose values are mostly aligned with yours but that does pathological things when it takes its values to the extreme. In this paper, we examine a similar process, but involving two (or more) agents rather than one.
For those of you who were also at the MSFP, you can read some additional discussion of the paper here. The main idea is that Connor is working on a simulation to help test the ideas in the paper. If you’re interested in helping with the simulation but don’t have access to the forum post linked above, get in touch with me.
]]>Their research has a fair amount of overlap with mathematical logic. I’d encourage any logicians who are interested in these sort of things to get involved. It’s a very good and important cause; the future of humanity is at stake. Unaligned artificial intelligence could destroy us all in a way that makes nuclear war and global warming seem tame in comparison.
Their technical research agenda is a good place to start for a technical perspective. The book Superintelligence by Nick Bostrom is a good starting point for a less technical introduction and to help understand why MIRI’s agenda is important and nontrivial.
One area of MIRI research that I find particularly interesting has to do with a version of Prisoner’s Dilemma played by computer programs that are allowed to read each others’ source code. This work makes use of a bounded version of Löb’s theorem. Actually, a fair bit of MIRI research relates to Löb’s theorem. Here is a good introduction.
Feel free to contact me if you’d like to know more about how to get involved with MIRI research. Or you can contact MIRI directly.
]]>Los niveles de los dos cursos seran un poco differentes, pero mucho de la material sera similar.
Las notas son aquí. Los subjetos son como sigue:
Esta material es más clasica, entonces hay muchas referencias posibles. Si no ha estado la teoría de grupos antes, recomiendo el libro de Fraleigh.
La mayoría de estas referencias estan un poco avanzadas. Yo he incluido dos referencias generales (por Tao y por Tao–Vu) que contienen mucho material fondamental — malafortunadamente, el libro de Tao y Vu no es disponible en una forma gratuita en la web.
Mi primera recomendación es las lecturas de Helfgott, “_Crecimiento y espansión en SL2″. _Primeramente, son en español(!) pero también comenzan a un nivel bastante fácil y, rapidamente, presentan un resultado muy importante de Helfgott sí mismo, sobre crecimiento en el grupo SL(2,p).
I recently had a chat with James Cummings about teaching. He said something that I knew long before, that being a good teacher requires a bit of theatricality. My best teacher from undergrad, Uri Onn, had told me when I started teaching, that being a good teacher is the same as being a good storyteller: you need to be able and mesmerize your audience and keep them on the edge of their seats, wanting more. Continue reading...
]]>However, we have a proof, a constructive proof that large cardinals are consistent. And they exist in an inner model of our universe. Continue reading...
]]>So, I'm fashionably late to the party (with some good excuse, see my previous post), but after the recent 200 terabytes proof for the coloring of Pythagorean triples, the same old questions are raised about whether or not at some point computers will be better than us in finding new theorems, and proving them too. Continue reading...
]]>If you don't follow arXiv very closely, I have posted a paper titled "Iterating Symmetric Extensions". This is going to be the first part of my dissertation. The paper is concerned with developing a general framework for iterating symmetric extensions, which oddly enough, is something that we didn't really know how to do until now. There is a refinement of the general framework to something I call "productive iterations" which impose some additional requirements, but allow greater freedom in the choice of filters used to interpret the names. There is an example of a classlength iteration, which effectively takes everything that was done in the paper and uses it to produce a classlength iteration—and thus a class length sequence of models—where slowly, but surely, KinnaWagner Principles fail more and more. This means that we are forcing "diagonally" away from the ordinals. So the models produced there will not be defined by their set of ordinals, and sets of sets of ordinals, and so on. Continue reading...
]]>But those people forget that \(0=1\) is also very true in the ring with a single element; or you know, just in any structure for a language including the two constant symbols \(0\) and \(1\), where both constants are interpreted to be the same object. And hey, who even said that \(0\) and \(1\) have to denote constants? Why not ternary relations, or some other thing? Continue reading...
]]>Somebody asked on the MathJax user group
To my understanding MathJax supports these input formats: LaTeX, MathML, and AsciiMath. If I'm making a website and I can choose to use any of the three formats, what are some advantages of choosing each?
Since I've answered this so many times, I thought it might be worth copying here:
"That's a tricky (trick?) question.
MathML is MathJax's internal format (essentially anyway) so anything that can be done in MathJax is done through our MathML support, cf http://docs.mathjax.org/en/latest/mathml.html. While MathML is quite good for such an internal purpose, it can be difficult to create. It's rarely written manually (much like HTML or CSS) and tools can have trouble producing highquality MathML (converters can fail, editors might produce overcomplicated MathML). MathML is the dominant format used in professional publishing workflows and thus comes with a rich toolchain out of XMLland.
MathJax's LaTeXlike input provides a faithful implementation of the most common mathmode LaTeX commands as well as other standard packages and a few nonstandard features, cf. http://docs.mathjax.org/en/latest/tex.html. LaTeX is much easier to author by hand than MathML and provides the typical LaTeX advantages such as custom macros (for even easier authoring). It also has the benefit of a large community thanks to the wide adoption of TeX as a programming language for print layout in academic writing. LaTeX is probably the most popular format when people have a choice, so MathJax's TeXlike input has a wide community out there. From a real TeX perspective, MathJax restricts LaTeX input to mathmode since it converts internally into MathML. Due to LaTeX's print heritage, some constructions are hard to do (e.g., equalwidth columns are trivial in MathML but not doable with the default LaTeX macros).
AsciiMath is a lightweight markup language designed to convert well to MathML. I sometimes like comparing it to markdown  not as powerful but much more sensible to write. It does not have the expressive power of MathML but it is very easy to learn because it was designed by Peter Jipsen specifically for highschool and collegelevel students. It is less frequently used but if it's expressive power is sufficient, I tend to recommend it.
In summary, MathML is MathJax's internal format so anything you can do with MathJax you can do with its MathML input. LaTeX is virtually as powerful (with some edge cases), is easier to author by hand, and has a large community both from real TeXland and MathJax's community. AsciiMath is the little brother of both MathML and LaTeX and provides a good compromise between expressive strength and human readability.
If you look beyond MathJax there are even more options, of course."
Moving on.
On the "Getting Math Onto Web Pages" community group, Tzivya raised a big topic regarding accessibility:
I would love it the world would come to understand that accessibility is a subset of machine readability. Accessibility APIs are a specialized kind of machine. If we are working on machine readable math, we need to make sure that those specialized machines can read the math too. Otherwise we will do the work twice.
I found myself disagreeing with Tzivya (which means I'm probably wrong because she is awesome). This disagreement is mostly influenced by our work at MathJax for the past year or so, making math rendering accessible via MathJax. But the point is an important one to me because, as I expected (feared?), a few discussion on the Community Group have already brought up the problem of looking for the right™ solution instead of the realistic one.
For me, what we have now is the right solution: HTML, CSS, ARIA, SVG etc, several competing math rendering/computation/etc implementations based on these, lots of tools tangential to them. An excellent kind of mess without standards beyond what works ok for each project out there. It's not the right™ solution but it has the potential of becoming better and better. It's really just another part of web development; nothing else needed.
Anyway, so I wrote:
"I do dream that eventually (maybe 10 years from now?) we'll have a thorough a11y API mapping for mathematics. At the moment, I don't think mathematics (as a culture / language) is ready for this (though web technology probably would be).
Regarding general machine readability vs accessibility, one important difference I see is that machine readability can benefit from partial results whereas accessibility cannot.
A typical example for this might be units. If we can find a way to make units machine readable, I think we'd have a major improvement for STEM on the web. But it won't help accessibility (much) to know that there are units in an expression if it is otherwise unintelligible.
Of course, we currently don't have any standard or best practice for exposing units on the web. The MathWG had a very old note on units (from 2003) which suggested class='MathMLUnit' on MathML elements; I don't think that's viable approach today. Perhaps schema is a better starting point considering how successful search engines can leverage units in recipes (I could imagine lab protocols and engineering might benefit from similar methods).
For some tools it's extremely easy to generate markup for units, e.g., Jos de Jong's MathJS has a rich interface for handling units and could probably easily expose them in a visual output. TeX has a rich history with the physics and siunitx packages (which are, for example, partially available in MathJax as third party extensions) and heuristics seem feasible to enrich formats in general (again, MathJax can do some of that via the speechruleengine).
I think for humans we have to change our expectations. Otherwise, we'll just end up repeating the mistakes of the past. I'll post some thoughts on the accessibility thread later."
And I then also wrote on the related thread:
"Today the most
reliable method is still to use binary images with alt text: static images
are the most reliable in terms of cross browser/platform/network conditions
for visual rendering and alttext is the only way to guarantee at least
some alternative rendering (e.g. aural and braille)  no matter how poor
the results may be.
Don't get me wrong, in many specific situation, there will be better ways.
If you have simple content, then you can get decent visual results with
HTML tags with nested arialabels. If you know you can rely on webfonts
(e.g., many ebook situations) then you can use CSS with webfonts for
rendering (and again nested labels). If you don't need IE8 (sigh) then you
can use SVG etc.
But in generality, binary images with alttext are still the most robust
way  and that's an extremely sorry state. I'm pretty sure we can do
better but we need to identify what users need and what tools can
realistically achieve today.
My first guess would be: some form of speech text, potentially enabling
some level of exploration through nesting (and perhaps full exploration via
JS). That's not as bad as it sounds. SVGs with arialabels are already a
close second in terms of usability (pending the ultimate demise of IE8),
and like HTML they open up the opportunity of deeplabels and thus already
get a certain level of exploration.
But there are other aspects. For example in the US, MathSpeak has a long
history and many users of aural rendering are trained to its way of
describing the visual structure of an equation. I've heard enough anecdotal
evidence to take this very seriously  after all, that's how visual users
do it. Still, a few months ago I learned that in Germany, on the other
hand, blind students might learn TeX syntax early in school (most likely
because there is no tradition like MathSpeak which, after all, precedes the
web by decades).
I also expect much overlap with SVG accessibility, where the challenges of
summary information at a top level and exploration of details are very
similar to mathematics."
Oh, I gave a talk for Global Accessibility Awareness Day 2016 at the FernUni Hagen  in German (it's been a while). The slides are on GitHub Pages. It's already somewhat outdated because Wikipedia now serves mainly SVGs (generate with mathjaxnode).
Anyway, the core summary stays true:
Why is it difficult to make formulas accessible?
 Formulas compress information (extremely)
 Formulas are often visual
 Formulas are contextdependent
 Formulas are poorly authored
In other words, math accessibility sucks bad. And no solution will really help you there. But MathJax now does its best to make it suck less.
Oh, speaking of accessibility, I'm extremely disappointed that I won't make it to role=drinks after all  but if you're close by, why don't you drop by?
]]>Anyway.
There was a joint meeting of CSSWG and DPUB IG on Monday and I was running late (discussing mathonweb things with Daniel Marques actually), so I missed the first 15 minutes. My mind was blown when, within 2 minutes of me sitting down, a motion was accepted to task Florian with spec'ing (specing? speccing?) out a media query for MathML support (as well as an API to flip it). I didn't feel I was in a position to speak up, so I just sat there wondering what just happened.
The motivation seems rather natural, I suppose. As long as there's no universal browser support for MathML, people are still stuck with providing fallbacks. In situation where they cannot load a JS library themselves (e.g., in ebooks), they have to use a fallback even if they could provide MathML.
If there was a media query, people could add both fallbacks and MathML in a standardized fashion, hiding one or the other depending on the result of that media query. In addition, an API would enable JS libraries to leverage a universal way to progressively enhance content; it wasn't quite clear in the end, but some people seemed to hope that API could additionally be triggered by assistive technology.
This discussion started (I think) on the epub3 end, where the IDPF is currently discussing epub 3.1 and best practices; as usual, MathML features in a painfully prominent role. In epub land, the dream seems to be: you create an epub3 file once and some day down the line, when a user's reading system finally picks up MathML support, the old content will magically improve  progressive enhancements so to speak.
Naturally, @supports
is already very helpful in all sorts of ways today which probably made it a nobrainer (and thus the quick decision). Unfortunately, I think a "media query for MathML" does not solve a single problem.
I was so late to the meeting so when the question for "any objections" came out, I did not feel I was in a position to do so. Still, in a breakout meeting later that day (about epub specifically), I voiced my criticisms to both epub, accessibility, and CSS people.
So this is, if you will, the written version of my opinion. (In case you missed that you are on my personal website, please note the use of "my" here.)
A single media query for MathML won't help me as content provider (author, publisher, technology specialist); I also find it generally unhelpful for the web as a whole.
The problem with a single query is simple: when would a browser respond positively? When should a browser legitimately claim to have MathML support? I honestly don't know.
MathML is a huge (and pretty vague) spec. There's not a single browser or library that could claim complete support. MathJax is the top scorer with 85% on the MathML test suite (since MathPlayer was kicked out by IE) but that's not saying much since the test suite is highly biased  whoever feels like it can submit the data, and in MathJax's case that was me (who is obviously biased).
I can't see how a single media query for all of MathML could provide people with any kind of reliable information on the frontend. Most likely, Gecko and WebKit implementations will immediately turn it on which does not help one bit  people will still have to test their content on those engines in detail.
Personally, I have already done that too many times (and keep a close eye on them) and I always come to the same conclusion: I cannot recommend using them to anyone since they are too unreliable. So I'm still stuck the same way I was before. Similarly, any publicly available crawler data I've seen indicates that nobody is using native MathML on Gecko and WebKit in the wild, so my position does not seem to be unique.
Of course, the CSSWG might spec out a whole set of individual media queries for every single MathML features. As unlikely as that seems, we'd just end up deeper in the rabbit hole: MathML is still extremely vague so few features are specified in enough detail (compared to CSS or SVG anyway). To take a simple example, while Gecko and WebKit might claim support for mfrac
(fractions), it's not helping me if those fractions are laid out badly as soon as I put something mildly complex in them. So again, I'll end up not using it.
In terms of accessibility, it seemed an API that assitive technology could trigger would not be as easy to implement in browsers (yet "easy" seemed a prerequisite given the comments from browser reps in the CSSWG). Since AT tends not to inject scripts (JAWS craziness notwithstanding), they'd need a more sophisticated feature (which is, I think, also being discussed by CSSWG, but considered much harder, i.e., unlikely).
Besides, this assumes that MathML significantly benefits accessibility. After MathJax getting deeply involved in building a suitable tool, I find this argument questionable. Talking to a11y folks, it usually comes down to "but MathPlayer!" and while MathPlayer was pretty good (albeit dead in the water now) it didn't actually use MathML but a proprietary internal format representing the result of semantic heuristics; this makes it kind of hard to use it as an example for how great MathML is for accessibility.
I think it's unrealistic to expect every single assistive technology to invest as much in a niche like math. I'd estimate that, at any one point in time over the past 18 years, the number of actively maintained accessibility tools with MathML support was 1 (no, neither JAWS nor VoiceOver count as "maintained" when it comes to MathML).
Further, not a single tool has ever used MathML as an internal format because it is simply insufficient  it is a XML document language for layout and is grossly unsemantic (and don't say "but ContentMathML" now).
If people feel like exposing MathML to AT, then they can use one of the many standard tricks to ARIAhide the fallback content and visually hide the MathML. Again, in my opinion, that's a disservice for your readers, but nobody stops you.
For me, the weirdest thing about this whole decision was its speed: that the CSSWG signed off on this idea in under 20 minutes just makes me a teeny tiny bit skeptical. It feels a lot like one big "whatevs"  browsers don't really care but, hey, a media query is little work and if it keeps these math people off our backs, all the more reason.
The real problem remains with or without a media query: where is MathML going? As Romain commented on twitter:
@pkrautz it's real progress going on
— Romain Deltour (@rdeltour) September 19, 2016
1999 → hope MathML gets implemented
2016 → hope a declaration of nonimplementation gets implemented
Browser vendors have never worked on MathML support, MathML is no longer maintained as a spec, the MathWG is no more (did you notice?), and MathML is a bad web standard for both layout (another post) and accessibility.
I think it's time to realize that after 18 years of not succeeding on the web, the problem might just lie with MathML itself. We don't need it on the web (CSS and SVG are better for layout and ARIA better for accessibility) and we should stop giving browser vendors an excuse not to do anything that actually helps those developers who realize math on the web in its myriad forms today. (And the XML document world, where MathML succeeded, would be better off as well.)
Don't get me wrong, there are many problems left for math on the web but MathML is not a silver bullet, in fact, it solves none of them. Even if it was implemented widely, we'd still need CSS and ARIA features to match. Instead of waiting for others (i.e., browsers) to solve their problems by magic, the few people with an interest (and the resources to match) will have to solve this niche problems on their own and in a way that moves the web forward as a whole.
Either way, a media query for MathML is pointless.
]]>Enjoy! Continue reading...
]]>I'm visiting David Asperó in Norwich at the moment, and on Sunday, the 12th, I will return home. It seems that the pattern is that you work most of the day, then head for a few drinks and dinner. Mathematics is eligible for the first two beers, philosophy of mathematics for the next two, and mathematical education for the fifth beer. Then it's probably a good idea to stop. Also it is usually last call, so you kinda have to stop. Continue reading...
]]>We consider the iteration of quasiregular maps of transcendental type from to . In particular we study quasiFatou components, whichare defined as the connected components of the complement of the Julia set.
Many authors have studied the components of the Fatou set of a transcendental entire function, and our goal in this paper is to generalise some of these results to quasiFatou components. First, we study the number of complementary components of quasiFatou components, generalising, and slightly strengthening, a result of Kisaka and Shishikura. Second, we study the size of quasiFatou components that are bounded and have a bounded complementary component. We obtain results analogous to those of Zheng, and of Bergweiler, Rippon and Stallard. These are obtained using techniques which may be of interest even in the case of transcendental entire functions.
]]>Our objective is to determine which subsets of arise as escaping sets of continuous functions from to itself. We obtain partial answers to this problem, particularly in one dimension, and in the case of open sets. We give a number of examples to show that the situation in one dimension is quite different from the situation in higher dimensions. Our results demonstrate that this problem is both interesting and perhaps surprisingly complicated.
]]>We study the class of functions meromorphic outside a countable closed set of essential singularities. We show that if a function in , with at least one essential singularity, permutes with a nonconstant rational map , then is a Möbius map that is not conjugate to an irrational rotation. For a given function which is not a Möbius map, we show that the set of functions in that permute with is countably infinite. Finally, we show that there exist transcendental meromorphic functions such that, among functions meromorphic in the plane, permutes only with itself and with the identity map.
]]>The obvious problem is: how should that work? How do we get this small, disparate, and sometimes divided community of math tools for the web to inform web standards and, ultimately, browser development?
Well, it's time to find out.
A couple of people have been working towards a new effort and we've now formed a W3C Community Group. The name may sound funny but it's what this group is after: Getting Math onto Web Pages. No fuss, no drama, no limitations. The focus is on how we do this today and how we can make it easier.
So now it's up to us.
If you're a developer of a tool that makes math work on the web today and want to help shape the future, then it's time to step up. I know your resources are probably tight, in fact most projects out there are run by idealists, as sideprojects or chronically underfunded. I hear you.
But you built a tool because nothing was getting the job done. Standards? Same thing. We need to learn about the process, understand what we want to do and what we can do, and ultimately, help build standards that work for everyone. Otherwise, the job won't get done.
So join the Community Group and work together to move the web forward for mathematics and beyond.
Need more information? Here's the initial description from the CG homepage:
There are many technical issues in presenting mathematics in today's
Open Web Platform, which has lead to the poor access to Mathematics in
Web Pages. This is in spite of the existing de jure or de facto
standards for authoring mathematics, like MathML, LaTeX, or asciimath,
which have been around for a very long time and are widely used by the
mathematical and technical communities.While MathML was supposed to solve the problem of rendering mathematics
on the web it lacks in both implementations and general interest from
browser vendors.However, in the past decade, many math rendering tools have been pushing
math on the web forward using HTML/CSS and SVG.One of the identified issues is that, while browser manufacturers have
continually improved and extended their HTML and CSS layout engines, the
approaches to render mathematics have not been able to align with these
improvements. In fact, the current approaches to math layout could be
considered to be largely disjoint from the other technologies of OWP.Another key issue, is that exposing (and thus leveraging) semantic
information of mathematical and scientific content on the web needs to
move towards modern practices and standards instead of being limited to
a single solution (MathML). Such information is critical for
accessibility, machinereadability, and reuse of mathematical content.This Community Group intends to look at the problems of math on the web
in a very bottomup manner.Experts in this group should identify how the core OWP layout engines,
centered around HTML, SVG, and CSS, can be reused for the purpose of
mathematical layout by mapping mathematical entities on top of these,
thereby ensuring a much more efficient result, and making use of current
and future OWP optimization possibilities. Similarly, experts should
work to identify best practices for semantics from the point of view of
today's successful solutions.
This work should also reveal where the shortcomings are, from the
mathematical layout point of view, in the details of these OWP
technologies, and propose improvements and possible additions to these,
with the ultimate goal of reaching out to the responsible W3C Working
Groups to make these changes. This work may also reveal new technology
areas that should be specified and standardized on their own right, for
example in the area of Web Accessibility.
The ultimate goal is to pave the way for a standard, highly optimized
implementation architecture, on top of which mathematical syntaxes, like
LaTeX or MathML, may be mapped to provide an efficient display of
mathematical formulae.Note that, although this community group will concentrate on
mathematics, many other areas, e.g., science and engineering, will
benefit from (and factor into) the approach and from the core
architecture.
PS: We've also applied for a CG slot at TPAC 2016 in Lisbon for a facetoface of the CG as well as the opportunity to talk to other groups. Fingers crossed!
]]>You can find the video here: Continue reading...
]]>I don't have any analytics on this site beyond what CloudFlare collects passively. There was spike of ~800 unique visitors and then higherthanusual traffic afterwards, it might not be completely unreasonable to guess that 1000 people opened the post back then  until somebody posted it to Hacker News today (no link to save your sanity from reading HN comments) so now it's more like 20,000 people have clicked a link to that piece. Of course, few of those will have read it, fewer still will have carefully read it. My best guess is: 3 people have read it. Does that sound about right?
Most responses were basically "meh" (especially on the twitters). Steve Faulkner is, of course, to blame for much of that twitter attention (thanks Steve!). I also received a few kind emails with responses, thanks for those. Elsewhere, Jesse McKeown wrote a short tumblr; as a former mathematician I'll formally (get it?) object to the use of Gödel's work.
Paul Topping's "response" was mostly focused on his own ideas which have little to do with what I wrote. Let me respond to those few points that were about my piece. Let's do this inline.
The first thing to note in his post is that he says that MathML is a failed web standard. By this, I believe he is only saying that it has failed as a language supported by browsers.
I had hoped my glorious <s>
tag was making the point clear. But I guess not.
He acknowledges that it is in heavy use in education, publishing, and elsewhere but I wish he’d made this distinction a bit more strongly.
Ignoring the point that I didn't actually mention education (or "elsewhere"), I thought I had fulfilled this "wish" when I wrote: It’s also clearly a success in the XML publishing world, serving an important role in standards such as JATS and BITS. The problem is: MathML has failed on the web.
.
I'm not sure how much clearer I can make that distinction  success here, failure there.
The browser makers ignore MathML so getting rid of it won’t affect them much. Perhaps Peter is directing his message to the MathML community itself.
For what it's worth (and before anyone needs to speculate), my piece was very broadly directed at the web community. I was probably looking for readers who follow current trends in browser standards and their development. (Shout out to Chaals!)
This one’s easy. MathML isn’t implemented in most browsers so its not used.
That argument seems rather simplistic to me. Looking at any successful new web standard out there today (e.g., picture, flexbox, grid, animation), even a partial, behindaflag implementation does not mean the standard is not being used. Instead, there's a positive feedback loop with (often seemingly small groups of) developers. Even at the best of times (e.g., Dave Barton pushing WebKit forward for a year, Fred Wang's crowdfunded months), developer feedback for MathML was (and is) nonexistent (cf. my example of serious bugs not even being reported).
Sure but imagine if MathML specified layout to the level that TeX does.
This is a) ignoring how badly Presentation MathML does not specify layout (in particular, compared to CSS) and b) a red herring (TeX).
This might well be the case but what’s the point here? If CSS now has what math layout needs, we’re done, right?
Yes. That's the main point, actually.
Perhaps, but even if Presentation MathML provided sufficient semantics, most authors wouldn’t add them. The fact is MathML already provides recommended markup patterns for expressing a lot of math semantics but authors aren’t interested in adding such patterns to their math. Authors generally stop tweaking their math as soon as it looks right and can be read by a fellow human. I don’t think this will change. Even publishers are less and less interested in spending resources on marking up math with the required level of semantics. This won’t change even if MathML added missing semantics constructs and the necessary editing tools were available. Instead, everyone is moving in the opposite direction, spending less and less time and money on careful authoring.
An elegant straw man argument is still a straw man argument. I did not write about authoring or extending MathML. Good points though.
Peter acknowledges Neil Soiffer’s work on algorithmically extracting semantic information from Presentation MathML but seems to think it has hit a brick wall.
Another case of putting words in my mouth. A bit farfetched this time, since MathJax is actively doing research in this area.
In technology, when someone has a better idea how to do something they should just do it and let the market decide whether their solution is really an improvement.
To quote myself:
Today, lots of tools will let you render mathematics using CSS.
It’s possible to generate HTML+CSS or SVG that renders any MathML content [...] on the server.[And obviously on the client as well.]
Since layout is practically solved [...].
I tried to make a point that CSS and SVG already provide various solutions today. I also tried to make a point that MathML is not used significantly in the wild (except by conversion to HTML/CSS or SVG of course). So it seems to me that I argued that "the market" has chosen these solutions over MathML.
But I guess I wasn't clear enough. Oh well.
No problem but a lot of work needs to be done first.
No, see above.
Peter claims MathML’s mere existence is blocking discussions. What discussions did it block?
That's a good point even though Paul's piece is a nice example of the point I was trying to make. Calling on the community (who is that again?) to magically fix MathML after 10 years without development instead of making room for successful solutions? That is an elegant block.
Anyway, one problem for me is that many discussions I have in mind happened privately, especially with web standards experts. But that's no excuse for not spending a few minutes thinking about public examples; for some reasons, this example the discussion on mozilla.dev.platform is the first to come to mind (man, I was feeling righteous back then).
Another example are the specs themselves. The ARIA spec basically has a big glaring hole where math should be. Similarly, take a look at the suggestions in the ARIA best practices spec and the epub3 spec. All of them focus entirely on MathMLbased solutions without any reflection on whether these actually work in real life. The ARIA practices spec even discourages working solutions like HTMLmath using dubious arguments about the semantics of Presentation MathML. Moving on.
Paul goes on to write about generating semantic information. It's not quite a straw man but nevertheless has little to do with my concerns about exposing semantic information on the web.
To wrap up.
Of course, Peter doesn’t believe automated semantics recognition can do the job.
See above.
Do we want that math to look identically in every browser? I believe the answer is generally “no”.
I have the impression people generally expect consistent rendering across browsers. But anecdotal evidence is, well, anecdotal.
And that's all folks. I'll add more as they come along.
And stay tuned for more.
Comments
Don Stolee, 20160414
Totally agree with your points raised and must admit don't understand all of it.
We are XML publishers out of Australia and use MathML within our markup. We then publish the XML content to our HTML5 eReader (tekReader) and use MathJax to assist with the rendering.
Example here: http://tekreader.eglootech.com/book/tekReaderGuide#part22#pt2211h3
It seems to work well on modern browsers found on desktops, tablets and smartphones and we have a University in Canada using our reader.
I would hope the XML world does not drop the standard and browsers continue to support, somewhat.
Peter, 20160414
Thanks for your comment. Tekreader looks very nice.
MathML is clearly a success in the XML world so I don't see it disappearing. I'm not suggesting that anyone should drop MathML if it works for them.
The point I was trying to make was entirely about its role on the web where other tools have made it obsolete (in the sense that it is no longer necessary to have native MathML browser implementations). Since most XML markup is converted to HTML for web delivery (e.g. OASIS tables), I don't see a huge problem in converting MathML to HTML as well.
Does that make sense?
Don 20160414
All good Peter. Thanks for getting back to me. If I may add. I've been providing XML publishing systems since the early 90's (SGML back then). All very monolithic and complex. With the advent of tablets and smartphones I see a trend in marking down XML (I call it dummy down) to HTML5. In fact my business now advocates markup using HTML5 (now with semantics) and do away with all the complexity downstream. Most of the rich markup is never used anyway (aka S1000D).
Peter 20160414
Thanks for the additional comment, Don. I'm far from your level of experience obviously, but I've also heard about this trend. In that context, I often point to John Maxwell's BiB 2012 talk.
Don 20160414
Awesome! Thanks for sharing. At least I know I am not crazy!
In particular a successful mathematical idea is polished with the dust of the many failed ideas that preceded it. Continue reading...
]]>I recently posted a terse  uhm, shall we say summary?  of my thoughts on MathML on a11ySlackers; and I promised a blog post. There's now a 6000 word thingie sitting in my drafts which would take months to whip into shape. So I tried again and it now feels both too long and too short; oh well, maybe it leads somewhere, maybe it doesn't.
Needless to say, opinions posted on my personal website are my personal opinions (funny how that works). In particular, they do not reflect the opinions of any of my clients, let alone the team at MathJax. I think they don't particularly help anything or anyone specifically except, perhaps, in encouraging a more open and realistic discussion.
MathML is a failed web standard.^{*}
We can do better, we deserve better.
MathMLinHTML5 is in the way of that.
^{*}Some people might prefer "browser standard", as in "a web standard to be implemented natively in the browser" since some web standards do not rely on browser implementations. Also, "natively" as opposed to some webcomponents hack shipped in a browser.
It doesn't matter whether or not MathML is a good XML language. Personally, I think it's quite alright. It's also clearly a success in the XML publishing world, serving an important role in standards such as JATS and BITS.
The problem is: MathML has failed on the web.
Luckily, many technologies have succeeded and today MathML is neither necessary but also no longer sufficient for math on the web. Instead of one monolithic solution, we have many. We should acknowledge this and move forward towards several newer and smaller standards that actually help developers.
Here are a few reasons that make me say these things.
You might easily think they do (Office! ChromeVox! VoiceOver!) but the browser vendors actually don't. The partial MathML implementations in Gecko and WebKit are entirely the work of volunteers. Largely unpaid, largely unsupervised, largely unaccountable.
Not a single browser vendor has stated an intent to work on the code, not a single browser developer has been seen on the MathWG. After 18 years, not a single browser vendor is willing to dedicate even a small percentage of a developer to MathML.
This is where the story should end, really. But sadly it doesn't. MathML's success in the XML world has kept it alive, but not for the benefit of anyone on the web.
MathML is a poor web standard and it would be better to remove it from HTML 5.
If you look at publicly available crawler data, you'll notice that it's hard to find examples of MathML that aren't behind paywalls. If you look further, you'll hardly find an example where people providing MathML content rely on native MathML implementations; even on Gecko and WebKit they use MathMLtoHTML5 converters. Another indicator is that, despite implementations having subtly deteriorated in the past two years, people aren't even complaining (I mean, WebKit stopped drawing surds (try this in Safari 8) but apparently nobody cared enough to even file a bug). Actual developer problems are so extreme you can't seriously develop anything slightly advanced with MathML (e.g., Gecko has nonexistent or incomplete support for basic APIs such as style, dataset, or event handlers for MathML elements).
Ok, truth be told, I don't know. The problem is: it's nearly impossible to generate good Content MathML (except with massive manual labor). As far as I know there is not a single significant collection of mathematics encoded in Content MathML out there. It's mainly ephemeral research projects and some handcrafted projects. That's fine, we need research after all, but that is not a standard fit for the web.
Now <mstyle>
, <mspace>
, <mpadded>
, <mphantom>
, <menclose>
, <mfenced>
, <mtable>
, <mstack>
might sound funny to a web developer but it's a serious problem. The web has found a productive separation of concern. MathML is incompatible with this approach.
MathML assumes an implementor would know or care about the intricacies and traditions of math layout. How do you draw a surd? Not specified. How do you draw a fraction? Not specified. How do you space things? Not specified. [But yes, dear implementor, you should support arcane mathematical layout features like movable limits, operator dictionaries, the subtle spacing and layout difference of inline and displaystyle and so forth; you know why they're important, right? RIGHT? And also make sure to implement 5 different approaches to vertical stacking, because, reasons  kthx, xxo.]
Today, lots of tools will let you render mathematics using CSS. It's messy but it works everywhere (ok, dear IE7 user, not for you, I'm sorry). The time when MathML implementations would have significantly enhanced web layout features are past.
Neil Soiffer wrote ingenious heuristics for MathPlayer which makes most people think that Presentation MathML makes mathematics accessible. That's about as accurate as saying OCR means all images with text are actually accessible.
The reality is that even for schoollevel math you need both highquality Presentation MathML (which is rare in itself) combined with powerful (but inevitably fallible) heuristics to extract meaningful semantic information; that's acceptable in the short run but not a real solution for mathematical semantics on the web.
MathML has seen no significant activity in almost a decade. In the industrial XML world, MathML is a success and people want more features but improvements are not even brought up. It seems nobody wants to jeopardize an adoption on the web. MathML being a web standard is negatively affecting even those users who actually embrace it because MathML is stuck in maintenance mode.
Did you know the MathWG's charter is running out this month? Would you notice if it wasn't renewed and the WG would cease existing? Would you notice if WebKit and Gecko ripped out their MathML implementation tomorrow? I'm not sure many people would.
Many people I've met have the mistaken impression that browser manufacturers have declared an intent to implement everything in the set of standards usually called HTML 5. They have not (even if HTML 5 as a "spec" may strive for that).
I think as long as MathML is in that set of standards, the lame duck argument ("it's a standard!") will continue to prevent alternative developments that help the actually working solutions for mathematics on the web.
At this point, MathML is effectively preventing mathematics from aligning with today's and tomorrow's web. This is hurting everyone. We need to drop MathML to make room for better standards.
It's possible to generate HTML+CSS or SVG that renders any MathML content  on the server, mind you, no clientside JS required (but of course possible). The resulting markup is arguably crap  it's span soup at its worst and some use cases are difficult to realize. But we've been there with HTML and CSS; people know how to solve this. It got us standards like flexbox and cssgrid; it's worth pursuing improvements to those standards that work instead of waiting for Godot.
It's also difficult to write your own math rendering tool. But we need more ideas, not less! It shouldn't be harder to write a simple math renderer in CSS or SVG than it is to write a RWD framework or a vector graphics library.
We don't need Presentation MathML for this even if many projects (like MathJax) use it as an internal format. MathML's failure as a web standard is hurting the web because it is blocking discussions about improving existing standards to help existing mathematics tools on the promise that eventually "MathML will solve everything (tm)".
I can't see a native MathML approach help to fill these final gaps. What existing rendering solutions need has little to do with what MathML implementations need. We don't need underspecified layout features tied to MathML elements, we need flexible CSS features that are integrated into existing CSS. Most importantly, existing solutions can iterate on partial improvements to ensure that these help layout on the web more generally, not just the needs of one specific mathematical markup language.
We don't need one true approach to math layout, we need flexibility for developers to be innovative and pursue new ways of solving layout problems and expressing mathematical thought on the web.
We need to get together with CSSWG/Houdini TF/etc to work out solutions that help those developers who actually solve the problem of math on the web.
To give a rough idea  From a MathJax point of view, three areas are difficult in CSS right now (and probably universally for math layout tools on the web):
Stretchy things are by far the biggest layout question, if only because they once led Ojan Vafai to call math layout fundamentally incompatible with CSS layout. As much as I respect his expertise, that cannot be the answer. It seems unlikely that we can't incrementally reduce the complexity for existing rendering solutions; in any case, it has little to do with MathML.
Since layout is practically solved (or at least achievable), we really need to solve the semantics. Presentation MathML is not sufficient, Content MathML is just not relevant.
We need to look where the web handles semantics today  that's ARIA and HTML but also microdata, rdfa etc. Especially ARIA is an extremely urgent problem because it currently ties mathematics entirely to Presentation MathML elements (where it fails) instead of providing a way to enrich all mathematical rendering on the web.
We also need to look beyond the semantics of mathematics into the semantics of mathematics in its applications, e.g., mathematical notation out of physics (units etc), chemistry (isotopes, reactions etc) and biology (trees, graphs etc). We need to find ways to expose this information to assistive technologies, search and other tools.
]]>You can find the article on the ESTS' website "Resources" page, or in the Papers section of my website. Continue reading...
]]>If you happen to be a student and a member of the Association for Symbolic Logic, you can apply for an ASL travel award. For more information as to how, please see here. There's just enough time to still submit your request! Continue reading...
]]>Some of you may have known him through MathOverflow as "Avshalom" where he often appeared in the comments with generally useful references, and some of you may have known him in real life as a teacher or a colleague, or a student. Some of you may have even knew him as Eoin Coleman. Continue reading...
]]>You can find that video right here: Continue reading...
]]>Not assuming the axiom of choice the definition of cofinality remains the same, if we restrict ourselves to ordinals and \(\aleph\) numbers. But why should we? There is a rich world out there, new colors that were not on the choicey rainbow from before. So anything which is inherently based on the ordering properties of the ordinals should not be considered as the definition of an ordinal. So first let's recall the two ways we can order cardinals without choice. Continue reading...
]]>MathML is often presented as the single solution to all math accessibility problems. For example, the ARIA spec says "Browsers that support native implementations of MathML are able to provide a more robust, accessible math experience than can be accomplished with plain text approximations of math", the IDPF accessibility guidelines says "[...] a benefit of native MathML support [...] is the ability to provide voicing based on the markup [...]" (ok, they do suggest fallback speech text later only to go on and tell you that annotationxml will work without, you know, some level of MathML support), even PDF/UA suggests MathML.
While this might seem plausible for authors, I can't shake the feeling that saying "just use MathML" is a bit of a cheat, especially on the web.
On the one hand, there's the reality of the technology landscape. I'm not going to criticize browsers yet again but accessibility happens to include visual rendering (duh!); without it accessibility of mathematics on the web is fundamentally broken. Even more so since ARIA fall short in terms of enabling HTML or SVG rendering of mathematics to be accessible.
On the other, while a growing number of screenreaders happily tout MathML support, there are (please correct me) really just three solutions out there: The new kids are VoiceOver and ChromeVox whose quality might be summarized with "meh" (not terrible but really not yet great in terms of math support or, for that matter, active development of math support). The grand old lady of math accessibility is of course MathPlayer which, I'm guessing, is the origin of the "just use MathML" ("just use MathPlayer"?) attitude for accessibility both because of its quality and because it is what many screenreaders leverage (JAWS, NVDA, Texthelp etc). However, with MathPlayer being pushed out of IE and into the status of a third party library (and integration into screenreaders sometimes lacking) that line of argument is a thing of the past. Practically speaking, there is no real, productive competition today and thus no resources for improvements.
Anyway, the question I've been pondering is: why do most screenreaders rely on external tools rather than implement MathML support themselves?
I suspect the answer is the same as with browsers: because it is too hard to render MathML accessibly. That is, while building on MathML is much better than alternatives (I'm looking at you, TeX), it's still an awful lot of trouble to write a decent (let alone good) MathML accessibility solution. Too much work, too much of a niche, too many other things to do, yadayadayada.
Of course with MathML I mean Presentation MathML since Content MathML is too rare in the wild. Presentation MathML is a very good XML format to canonically represent most traditional (read: print) formula layout and is universally appreciated as an archival format. But Presentation MathML is not "trivially" accessible. Unlike, say, ARIA roles, there is no straightforward process that will tell you how to, e.g., voice, sensibly explore or highlight a wellwritten MathML expression (let alone a shoddilywritten one). Instead, existing tools end up guessing both the mathematical structure of an expression as well as its semantics.
On the one hand, there's the fundamental problem of context (e.g., to tell whether (a,b) describes an open interval, a point in the plane, or an inner product) and of compression (Kill Math anyone?). But what's even more confusing about "just use MathML" is that, in fact, Presentation MathML can be pretty semantic  with elements like mfrac
, mroot
, or mlongdiv
, and things like menclose
notation, fences, or the operator dictionary, all of which carry semantics despite Presentation MathML being "just" about layout.
So you might think that's not so bad after all. However, that's only half true. Besides the obvious problem of virtually everything missing in terms of notation, Presentation MathML is somewhat lacking in genuinely neutral layout features. So as an author, you'll have to use those semanticbutreallylayout elements. This way you end up finding suggestions in the spec itself to use mfrac
with linethickness="0"
to represent a binomial coefficient.
$$$$
Which is visually rather similar to doing a construction using an mtable
(which might in turn be used to convey a vector/matrix).
And then you could also hack something together using mstack
which might sound like a fundamental math layout element (a vertical stack) but unfortunately is designed only for written addition, multiplication, and division.
As an accessibility tool you need to build in something that allows you to guess the semantic structure. And just to stress this again: not for the horribly broken markup you'll inevitably run into but for high quality, specsuggested markup.
Don't get me wrong. It's great that such heuristics are actually not impossible for Presentation MathML (as opposed to handling a programming language like TeX) so you can at least cover the educational use cases pretty well. But we're a long way making math accessibility being an average task for screenreaders (which is what it should be, just like visual rendering should be a simple task for a browser). MathML is a step forward for math accessibility but it is, ultimately, a tiny step given the practical problems, especially on the web. Endlessly repeating "just use MathML" is not helping.
I feel like I should add a Disclaimer to this one. We're currently building an accessibility solution for MathJax based on improvements to ChromeVox's math engine so obviously I'm terribly biased and a horrible person. But you already knew that.
]]>So I raised a question in the comment, and got replies from two other people who kept repeating the age old silly arguments of what are the elements of \(\RR\times\RR\) or what are these or that elements. And supposedly the correct pedagogical answer is "It does not matter what are the elements of \(\RR\times\RR\)." With that I strongly agree, and when I taught my students about ordered pairs on the very first class of the semester, I made it very clear that there are other ways to define ordered pairs and that we only do that because we want to show that there is at least one way in which ordered pairs can be realized as sets; but ultimately we couldn't care less about what way they encode ordered pairs into sets, as long it is a "legal" way. Continue reading...
]]>So here is how I read a paper, and I'd like to ask you to think about how you read a paper, and why you read it this way. Continue reading...
]]>Around the time when I first came to grips with the part of my job for MathJax which can only be called something horrible like "technology evangelist", webplatform.org launched. For a newbie like me this seemed like a big thing. All the big companies involved, supposedly working together, pushing the Open Web Platform, bringing together the best of existing devloper docs (Mozilla, Google, Microsoft etc), creating documentation hackathons etc. This is huge! (No it wasn't.)
So as a new MathJax and thus MathML "evangelist" I was dismayed that MathML was not mentioned in the "hot topics" list on the frontpage (cf. the Wayback Machine). I remember trying to raise the issue and getting a response literally years later (2014) pointing me to where I should have tried to start a discussion. Recently, I visited the site again, and since its redesign last year, it's a bit clearer where things stand, but still MathML is hard to find.
In fact, I can't find any link to MathML while browsing webplatforms.org. Only the search finally yields a link to the base page for MathML (and the content you'll find starting form there seems to be copied from MDN (which is obviously fine)). But don't worry, even here you'll find a little bit of MathML bashing.
So as I came upon webplatform.org again recently, I started to wonder why I had given up on approaching such sites. And it's pretty simple: if you look around, it's pretty much the same thing everywhere.
Whether it's the html5iscool sites like html5rocks or html5please, MathML just doesn't show up. General web development sites? Oh look, Smashing Magazine has no mention since 2009 and A List Apart has one comment in 2013 and even that 2009 article comes with snark..
I'd give you that caniuse lists MathML but even if you can bear the pain of looking at all that red, take a look at its frontpage which lists MathML under "other", a miraculous category with anything from EOT to strict mode to ShadowDOM; not exactly prime real estate.
Then you cast your net wider and go to Google Web Alerts and your register to get an alert for MathML, you set it to its widest setting – and what you'll get is almost exclusively a long lists of MathML snippets produced by Springer OA journals, with maybe some MathJax or StackOverflow sprinkled in. Speaking of which, don't go search for mathml on StackOverflow because you will only see questions that have next to nothing to do with the web (except that really nice and difficult one that obviously has to have negative votes – yay SO community...).
But maybe you are also interested in other things. Like regular web technologies (you know, the ones that get implemented by browser vendors) or other niche web ecosystems. And then you might just notice some really cool resources in those areas. Can you even imagine something like flexbugs or an awesomestyle GitHub list or the incredible 99problems for MathML? I admit I can't.
Let's stop here.
]]>A while back Tim Arnold, the awesome person behind projects like plastex and mathjaxserver asked the following question on the MathJax User Group.
I am trying to decide what font to use for MathJax. The TeX font is the default, but I think I remember that the STIXWeb fonts have the best glyph coverage.
I have a lot of math to support on all kinds of browsers. What factors should I consider when choosing the best font to use in MathJax?
Soon thereafter, fellow Booles' Ringer Dana Ernst asked me the very same thing. At that point, I was hooked and started this post. It only took me a month to actually get around to finishing it because I wanted to include a basic demo.
tl;dr. Font pairing is an art, is a pain, is an art. I've cooked up a small example on CodePen that allows you to test Google fonts with various MathJax fonts. Just grab a font name from Google Fonts, paste it in and check out how the available math fonts pair up. For screenrealestate reasons you might want to head over to CodePen. Easy as that.
See the Pen MathJax Font lab by Peter Krautzberger (@pkra) on CodePen.
It is a complex question because, essentially, font pairing is an art. If you simply look at existing sites that try to help you with this, it's clear that many people are looking for solutions while fully realizing that this is highly arcane design knowledge. Alas, I have no such knowledge. What I can add is that it's also a compromise between overall design and the effects on MathJax functionality. So let me summarize some of the important details.
The biggest limitation is obviously that MathJax only supports a handful of fonts. That's a bummer and we hope to add support for more fonts so if you're savvy and interested in helping out, reach out!
The next thing worth pointing out is that MathJax already goes a long way by matching the exheight and emwidth of the surrounding font, that is the height of x
and width m
. That's simply best practice but more work on the web.
However, it's usually still important to pair the math font with the surrounding font carefully to avoid disrupting the reader's flow between math and nonmath (because exheight/emwidth are often not enough matching, especially for upper case letters). Of course, you could use the math font for the surrounding text to avoid that but most people strongly favor their options for text more (and rightly so, mathematics should always serve the text in my opinion).
(Edit, 20151001 Davide Cervone had to correct me there. originally this had emheight, height of x
and m
, ex/emheight; D'oh...)
The next important thing is usually another piece of font functionality. That is, most people like to weigh their options with respect to font coverage, i.e., which Unicode points are covered by glyphs in the fonts. For that it's important to consider what happens if MathJax encounters a Unicode point that's not in the glyphs of the configured fonts.
For the default MathJax "TeX" fonts (for historic reasons), there's an additional feature: MathJax supports a wider range of Unicode than the fonts themselves might tell you upon inspection of their glyphs. That's because MathJax builds some characters on the fly (e.g., the TeX fonts do not include a quadruple integral but build it out of two double integrals; similarly for "negated" characters). If I recall correctly, we only do this for the "TeX" fonts (the release that added the additional webfonts was simply subpar for various unfortunate reasons, I'm afraid, and we never got around fixing it).
Next, MathJax will run through a (pretty complex) fallback chain within the configure fonts (e.g., upright Greek will be substituted with italic Greek because we think that's better).
Next, MathJax will ask the browser for a glyph, i.e, fallback to system fonts. Side fact: this also triggers reflows as MathJax has to measure the actual glyph as best it can (for the configured fonts, we generate the relevant data during production and load them on the fly but there are no browser APIs to get the relevant metrics for unknown fonts/glyphs).
The lack of exact information about an unknown glyph means that the layout can't be as precise as it is with our supported fonts. However, in many situations this is not a huge issue as such glyphs are usually rare and not part of complex layout situations. Then again, e.g., placing sub/supscripts can be affected so your mileage may vary.
The bigger issue (speaking from the complaints we get) is the randomness of the system font. You can control that via the undefinedFamily
configuration option of each MathJax output processor. You might then also add a separate webfont for that fallback (well, if you can find one that helps with your content and both fonts for math and text; a tall order usually).
Finally, by testing / preprocessing your content via MathJaxnode (for QA or for actual output), you can gather up the information on the missing glyphs for your content.
In the future, we are hoping to find the resources to expand the fallback cascade. The idea is to enable you to specify other supported fonts before the system fonts are used (e.g., use TeX fonts but then be able to fallback to Latin Modern or STIX). This would resolve the problem of measurements / layout quality but adds load (both webfonts and fontmetric data). In that context, we would probably work on simplifying our dev tools so that developers can build their own cascade. Finally, we would also hope to simplify our tools for generating the fontmetrics data, i.e., enable developers to modify a copy of MathJax to use their own inhouse fonts. But there are some technical requirements to the fonts and considerations for a smart fallback chain so that's highly nontrivial to set up.
In any case, you can play around with the pen and let me know what you think, either here or on CodePen.
See the Pen MathJax Font lab by Peter Krautzberger (@pkra) on CodePen.
]]>We construct a quasiregular map of transcendental type from to with a periodic domain in which all iterates tend locally uniformly to infinity. This is the first example of such behaviour in a dimension greater than two.
Our construction uses a general result regarding the extension of biLipschitz maps. In addition, we show that there is a quasiregular map of transcendental type from to which is equal to the identity map in a halfspace.
]]>So I figured, why not use this for explaining mathematical theorems. Continue reading...
]]>The case for support document from my grant application gives details of this conjecture, its importance, and the strategies that I hope to employ to work on it.
Excitingly, the university has agreed to fund a PhD student as part of this research. I just drafted a short description of what the PhD would be about, and I’ll post this below. (Note that this description might be edited a little over the next few days. In any case, it should give an idea of what the project will be about.) If you are interested, please get in touch!
]]>This programme of research is within the study of finite group theory (although some investigation of linear algebraic groups may also be involved). The aim is to prove, or partially prove, the Product Decomposition Conjecture which concerns “conjugategrowth” of subsets of a finite simple group: roughly speaking, given a finite nonabelian simple group G and a subset A in G of size at least 2, we would like to show that one can always write G as a product of “not many” conjugates of A.
This notion of conjugategrowth has interesting connections to many interesting areas of mathematics, including expander graphs, the product growth results of Helfgott et al, bases of permutation groups, word problems and more.
In the process of working on this conjecture, the student can expect to learn a great deal about the structure of finite simple groups (especially the simple classical groups) and, in particular, will study and make use of one of the most famous theorems in mathematics, the Classification of Finite Simple Groups.
We find a similar concept in Zelda's poem "Every man has a name" (לכל איש יש שם), which in Israel is closely associated with the Holocaust and with assigning numbers to people. But alas, we are all numbers in some database. Our ID numbers, employer number, the index under which you appear in the database. You are your phone number, and your bank account number. You are the aggregation of all these numbers. And more. Continue reading...
]]>Richard Feynman, who was this awesome guy who did a lot of cool things (and also some physics (but I won't hold it against him today)), has a famous threesteps algorithm for solving any problem.
Do not worry about your difficulties with MathML; I can assure you that mine are still greater.
I have written about why I care about MathML and why I care about Native MathML. Time to talk about some of the problems I see.
This piece reflects my personal opinion and is not indicative of the position of any project I might work on. It is meant as a conversation starter.
I care very much about MathML and in particular the mission of the W3C Math Working Group to facilitate and promote the use of the Web for mathematical and scientific communication. Yet, while MathML has succeeded everywhere else, it struggles on the web. That worries me.
MathML did not start out as an XML language but as the <math>
tag in HTML3. It was the browser vendors (Microsoft, Netscape) who rejected it; as a result, <math>
went into XML "exile" (where it was immensely successful) and returned to HTML in HTML5.
Still, all OWP technologies stand and fall with the support and adoption from browser vendors. It does not matter how good (or bad) a web standard is or how well it works elsewhere. Browser vendor adoption is the only relevant measure.
It's been two years since I started to write "MathML forges on".
Back then, native browser support seemed to be on the tipping point. Dave Barton had done amazing work on improving Alex Milowski's WebKit code, the deactivation in Chrome seemed to be a hiccup due to one single bug (that already had a fix). It seemed, with a little luck, Gecko/Firefox and WebKit/Safari would have made it to the 80/20 point within a year, hopefully in turn get the Blink/Chrome team to reenable MathML; then we'd watch as Trident/IE (now Edge) would hurry to integrate the math support from LineServices.
Two years later, Gecko has moved sideways, WebKit has barely moved, Trident/Edge remains a mystery, and Blink is "the villain" (for dropping the WebKit MathML code). MathML is still the only viable markup language for mathematics (recently reaffirmed by its ISO standardization), and yet, native browser support seems just as far away as ever.
Why?
Gecko's and WebKit's (still quite partial) support has been almost exclusively implemented by volunteer contributors (and mostly unpaid volunteers at that).
Effectively, no browser vendor has ever worked on MathML support in their browser. (Yes, that's a bit unfair to Mozilla devs who are great  sorry. There are also good people at Apple, Google, Microsoft; still, the companies all fail to invest in MathML browser support.)
The volunteers, on the other hand, come and go. Nobody is able to find significant funding and development is, once again, effectively dead.
At this point, I don't see how we can ever get sufficient native MathML support in browsers; the volunteer method does not work and the vendors remain uninterested.
The fact that browser vendors do not implement MathML says virtually nothing about MathML. Studying past discussions, it's clear that there isn't a lot of knowledge about the spec or the requirements of mathematical layout. (Again, this is a little unfair to some Mozilla devs.)
So I see no reason to give up on MathML, let alone math and science notation on the web. Because one thing has not changed: it's still the best markup for math  and education, industry, and research need a good markup that works on the web.
While I don't think native browser implementations is a realistic goal at this point, I think MathML can still be a trail blazer, especially for scientific notation. It is, after all, a long standing W3C standard and we know it works very well in a browser context (even if you need polyfills).
I think there are two problems we can focus on that are just as useful to move scientific markup (and the web in general) forward:
As opposed to native browser support for MathML, both of these are extremely feasible.
For the first, it recently became clear to that modern browsers (IE9+) are actually good enough for layout; that is, you can write converters from MathML to HTML or SVG markup so that the result is stable, i.e., provides the same layout on all browsers (comparable to TeX quality but naturally integrated into the page context). To be clear, this is not (just) about clientside rendering like MathJax (in fact, MathJax does not provide this yet).
The biggest problem is that the necessary markup itself is messy, making it hard to generate (just look at the spansspansspans that MathJax currently generates).
But is this unusual? I think this situation is not unlike how grids using Bootstrap or Foundation are overly complicated compared to grids using cssgrid layout. Or how doing flexboxlike layout is horribly complicated without flexbox.
I think we should focus on widely implemented standards and work on improving them so that the markup you need for good math layout becomes cleaner and thus easier to generate (both in terms of structure/semantics and performance).
For the second point, looking at the developments of the semantic web, it's obviously not being realized in terms of mandated HTML tags or CSS properties. It is being realized via ARIA roles, RDFa, microdata etc. I'm not saying these approaches work for the semantic structure of MathML (let alone STEM in general) but something along those lines seems achievable.
Frankly, I'm a bit tired of waiting for Godot native browser support for MathML. MathML is frozen because we're all waiting for browsers to catch up. It is simply not happening. Let's look for ways to move forward.
Comments
gimsieke, 20150810
Nobody is able to find significant funding
MathJax has managed to attract a significant network of donors. Why don’t they either encourage their “investors” to also invest in native math rendering, or why don’t they use the proceeds to fund native development directly? This shouldn’t be beyond their bylaws.
Peter, 20150810
Why don’t they either encourage their “investors” to also invest in native math rendering,
The "nobody" includes MathJax. Of course, the fact that we failed does not say much. The fact that everybody failed so far, might.
why don’t they use the proceeds to fund native development directly
Because then we wouldn't be able to develop MathJax itself.
This shouldn’t be beyond their bylaws.
Sure. Neither would be curing cancer.
Bruce Miller, 20150810
Interesting blog post! I've two comments to make.
Easy one first: I feel like you are unnecessarily harsh on the quality of Gecko's MathML support. While I understand your pride in MathJax, I'd still put Gecko at 90/10 or better rather than 80/20 or below. It certainly can use improvement and is more variable, depending on system fonts, etc, and I'd definitely appreciate more official support from Mozilla. But it gets all the essentials and with the right fonts looks virtually as good as MathJax  and it's blindingly fast in comparison.
This is more than a fanboy stance: I think there's a psychological factor to this as well, when the message seems to be that no matter what is done, it's never good enough.
The second issue is a bit more subtle. On the one hand, you advocate strongly for MathML; on the other, you propose to focus on "widely implemented standards" for doing mathematical layout. There seems a big ambiguity there: Are you suggesting that authors should create & serve MathML in their web pages and that the way forward is in improving and using the better supported standards as a way of rendering the MathML? Or are you suggesting using whatever technology is available to render something that looks like math, whether or not the representation is MathML? I suspect the former, hope for it, but whichever stance you take, I'd prefer to see it more explicit. The ambiguity just feeds the suspicions about MathJax in some and provides an excuse to abandon MathML in others.
Thanks for the thought provoking article;
bruce
Peter, 20150811
While I understand your pride in MathJax, [...]
This post is really not about MathJax. In many ways, the opposite. But the only ones who could claim pride in MathJax would be Davide and Robert; certainly not me.
I'd still put Gecko at 90/10 or better rather than 80/20 or below
I've often described Gecko as the baseline for MathML feature support. If you can't make your MathML work in Gecko, you probably shouldn't be using it.
But I also understand why people disagree with that. In my experience, you need to be quite knowledgeable about Gecko's implementation (at least from the outside) to avoid running into layout quirks or missing features; watching the MediaWiki math extension feedback is a good example for this.
Of course, this is nothing special, the same is true about MathJax. But the problem is that no large scale MathML adopter I've ever talked to is willing or able to spend the resource on optimizing their content for Firefox.
[...] depending on system fonts [...]
That's not a minor issue though. The switch to MATH tables has brought quite a few problems in terms of layout and more importantly developer burden.
While MATH tables seem to be the way to go, they can only be leveraged by native implementations (and there aren't exactly many fonts with MATH tables, nor would I expect that expensive niche to grow much soon).
This adds to the burden of front end developers who would have to provide two sets of webfonts  one for Gecko and one for everyone else (i.e., polyfills). It's another case of a good standard being useless because it's not widely implemented. But it's made worse because polyfills cannot leverage it so there's no positive feedback loop.
it's blindingly fast in comparison.
Sure. That's why I'm not talking about clientside rendering here but for the generation of HTML with CSS. This includes tools like LaTeXML or pandoc or any XML workflow tool.
(But fun fact: we've seen edge cases of clientside MathJax outperforming Firefox by a clear margin. I got lucky and was able to mention it to Rob O'Callahan personally and Gecko got improvements.)
I think there's a psychological factor to this as well, when the message seems to be that no matter what is done, it's never good enough.
I don't think the problem is "never good enough". MathJax is certainly not "good enough" for many people (in particular in terms of performance, but also layout, feature support etc).
I think the problem is rather "no chance of getting better". There is no interest from the browser companies; that's what would have to change.
I think even a limited implementation would be interesting if developers had the promise that bugs will get fixed and implementations moved forward. This is not some kind of chickenandegg problem, it's simply a failure of browser vendors (and just to repeat myself: not of individual browser developers!).
Are you suggesting that authors should create & serve MathML in their web pages and that the way forward is in improving and using the better supported standards as a way of rendering the MathML?
Or are you suggesting using whatever technology is available to render something that looks like math, whether or not the representation is MathML?
Neither and both. Authors should use whatever works for them. If that's asciimath during authoring or even in the final page, that's fine; I don't lose sleep over it. (Just like nobody loses sleep over somebody converting markdown in the page.) I do think that authoring tools and converters should not stop at MathML but think further because waiting for MathML support to come around is not helping.
I would like to see those tools move MathML forward by making it the best markup for rendering math on the OWP. But I'm not thinking of something that "just" looks like math but about HTML or SVG markup that is enriched to be just as powerful as its underlying MathML. That's currently not possible for lack of, e.g., aria roles. But I think wecould quickly get to a point where a fully equivalent "interpretation" (or "transpilation" to use a fashionable term) in HTML or SVG does not require clientside rendering.
The ambiguity just feeds the suspicions about MathJax in some and provides an excuse to abandon MathML in others.
This reads like FUD to me.
My piece opens with "This piece reflects my personal opinion and is not indicative of the position of any project I might work on." This obviously includes MathJax.
MathJax is a MathML rendering engine. I'm proposing to something based on MathML and my hope is to move MathML forward despite the lack of interest from browser vendors.
But if somebody needs an excuse to "abandon" MathML, I'd prefer to convince them by showing them how great MathML is rather than saying "oh, just wait a few more years and browser vendors will finally get it and implement it". MathML deserves better!
Bruce, 20150812
This post is really not about MathJax.
Understood. But really my point was that both Gecko & MathJax, while both imperfect, do pretty decent math typography, at least by the measure of web typography generally.
Sure. That's why I'm not talking about clientside rendering here but for the generation of HTML with CSS. This includes tools like LaTeXML or pandoc or any XML workflow tool.
... and ...
I would like to see those tools move MathML forward by making it the best markup for rendering math on the OWP. But I'm not thinking of something that "just" looks like math but about HTML or SVG markup that is enriched to be just as powerful as its underlying MathML. That's currently not possible for lack of, e.g., aria roles. But I think we could quickly get to a point where a fully equivalent "interpretation" (or "transpilation" to use a fashionable term) in HTML or SVG does not require clientside rendering.
...
The ambiguity just feeds the suspicions about MathJax in some and provides an excuse to abandon MathML in others.
This reads like FUD to me.
FUD? Perhaps, but the fact that I'm paranoid, doesn't mean that I'm not being followed. :>
MathML offers a representation of math in such a form as to enable: highquality rendering; accessibility; reuse (especially content). One would have hoped for gradual adoption & implementation of MathML, starting with the aspects that are both "easiest" and most in demand: rendering first; increasing support for accessibility; and eventually support for reuse. That seems to me a critical evolutionary path if true accessibility and reuse of mathematics will ever be achieved.
Alas, math is a niche; generating good MathML and rendering it is nontrivial, content moreso. And, as you point out, browser support seems stalled, at best.
While your proposed solution of improving HTML+CSS, RDF and aria seems practical and innocent, without a strong and simultaneous call for continued improvement of native MathML support in browsers and its generation by authors as well as the actual serving of MathML, there's the danger of undermining that evolutionary path of MathML support. I don't believe that's your intention, but the implication that authors need only serve HTML+CSS for rendering, imagining they'll someday add aria annotation, eliminates the most pressing reasons for wanting MathML in the first place. Reuse of mathematics, or even truly useful accessibility remain mere pipedreams.
...
But if somebody needs an excuse to "abandon" MathML, I'd prefer to convince them by showing them how great MathML is rather than saying "oh, just wait a few more years and browser vendors will finally get it and implement it". MathML deserves better!
Thanks; That's what I was hoping to hear. I just want to make sure that message doesn't get lost in the shuffle. If we give the impression that rendering and a modicum of accessibility is "good enough", we may as well just leverage the browser's improvements in image rescaling, attach little taperecordings to the images, and call it done.
Peter, 20150812
Thanks, Bruce.
While your proposed solution of improving HTML+CSS, RDF and aria seems practical and innocent, without a strong and simultaneous call for continued improvement of native MathML support in browsers and its generation by authors as well as the actual serving of MathML, there's the danger of undermining that evolutionary path of MathML support.
I disagree. As I wrote, I don't see any practical interest from vendors towards implementing MathML. So calling for improvements is pointless  they are not doing anything.
I'd be thrilled to be wrong and see browser vendors dedicate the necessary resources to MathML development (and maybe join the MathWG to help move the spec forward).
But if I'm not wrong, then "Waiting for Improvements" will be worthy of Beckett.
As much as I care about MathML, I care even more about mathematics on the web. Since native MathML support is not happening, I think MathML needs to evolve into something that can be native. My suggestion voiced here is that it should evolve towards HTML and CSS.
but the implication that authors need only serve HTML+CSS for rendering, imagining they'll someday add aria annotation, eliminates the most pressing reasons for wanting MathML in the first place.
I think "eliminates" is misleading. First, I disagree because you cannot "eliminate" what's not there. MathML is not usable on the web (without polyfills) because browser vendors are not supporting it.
Secondly, I disagree because I believe that only MathML will allow us to move towards "HTML as powerful as MathML".
That's the whole point of this piece, really: imho browser support will not happen, so let's think about ways how the spec (and maybe even the MathWG) can evolve to fulfill its mission.
And I obviously and strongly believe that MathML is the best basis for doing so.
But unless somebody can get browser vendors to dedicate the necessary resources, then I find it unhelpful to sit around and pretend like MathML is working out on the web. Instead, we should think hard about how it can be made to help math and science on the web (without native MathML implementations).
Reuse of mathematics, or even truly useful accessibility remain mere pipedreams.
Again, I disagree. On the one hand, it is really pretty easy to achieve exposure of the underlying MathML  just look at what ChromeVox did already years ago with MathJax, leveraging the internal MathML to enable fully accessible exploration of the visual output.
On the other hand, I think "reuse of mathematics" is too broad. I think quite a few use cases that people hope for are unrealistic (e.g., copy&paste has so many challenges on the web, with or without MathML). And the realistic ones (e.g., accessibility, search) can be achieved in HTMLifiedMathML (pretty easily, I think).
As much as I care about MathML, I care even more about mathematics on the web. Since native MathML support is not happening, I think MathML needs to evolve into something that can be native. My suggestion voiced here is that it should evolve towards HTML and CSS.
Bruce, 20150812
As much as I care about MathML, I care even more about mathematics on the web. Since native MathML support is not happening, I think MathML needs to evolve into something that can be native. My suggestion voiced here is that it should evolve towards HTML and CSS.
Just to be sure I understand, you're suggesting that rather than
<mfrac><mi>a</mi><mi>b</mi></mfrac>
the "New MathML" would be
<span class="mfrac"><span class="mi">a</span><span class="mi">b</span></span>
with perhaps a few `style="..."`` thrown in?
thanks;
bruce
Peter, 20150802
No. But probably for very different reasons than you might think.
But I'm not very interested in discussing technical details here. This is a conversation starter, not a technical document. If MathWG wants to consider this direction, then I think we need to bring together practitioners first. And that's practitioners who deal with rendering MathML in a web context; that's not exactly a strong suit of the WG today.
I also need to slightly correct (or extend) my previous comment to include what I mentioned in the post: I might prefer HTML but I also think SVG should be an equal target. For example, your LaTeXML can already generate SVGs for MathML; why make it less useful than it could be if you already have good underlying data in the form of MathML?
In general, while I do find it entertaining to think about god, afterlife, or a concrete mathematical universe, I find more comfort in the uncertainty of existence than I do in the likelihood that my belief is wrong, or in the terrifying conviction that comes along with believing in something (and everyone else is wrong). Continue reading...
]]>Oh, permalinks. The name is so clean and yet so misleading. WordPress is so forgiving to both admins, authors and visitors. But leaving that paradise is fun, too. At one point I had renamed all posts in a way which led to a site with zero posts; hilarious.
I've switched to the simplest permalink structure  enumeration. But then the question was: how many digits (I like my numbers to be the same string length)? I ended up with four digits. This is No.181 after 5 years of writing on the web, so it seems rather unlikely I'll reach 9999 in my life time. And if I do, I'd be happy to revisit this (@future self: sorry! it'll be a pain!).
I've been discussing the changes with Sam over the past few months. The biggest point of disagreement has been comments. Jekyll can't provide comments (obviously) and I am not interested in going back to Disqus (for various reasons). I also had the impression that comments were not doing it for me anymore. The ratio spam / useful comment was about 1000 to 1. Sure, Akismet took care of this and Disqus could, too. In addition, I'd get comments from other places (twitter, g+ or plain email) and since I'm not a cool indieweb dev it's never that many, I manually added them to posts.
In other words, I started to feel like comments are just not that useful anymore (caveat lector: see below) and that having a special technology for it seems overkill.
So for now, I'm going with commentsbyemail, with a simple link at the end of each post, prepped with a subject line for you. Comments will then be added by myself. I'm hoping anybody willing to comment is willing to send me an email (anonymous or not). Maybe I'm wrong. I'll also pull in comments from other places (e.g., twitter). There's currently a hypothes.is optin as well. Not sure if I'll keep it though. Feedback would be nice.
As always, xkcd.com/1357 applies. If you really feel the need to comment, please do it on your own site.
Having to do a lot of manual editing of my own work was a healthy experience. Yes, it drained time and varied from cringeworthy to depressing. But it also showed me that, once in a while, I still like my old writing. It also showed me some horrible crap, including one troll post which I'm keeping to remind me never to troll again. I hope it's the only one 😞.
I was surprised about the number of comments. One reason to go with email comments was the general lack of comments. Why keep extra technology on the site when I only get spam comments? But I admit I was surprised by the many (real) comments I have from my postdoc days and especially from other Booles' Ringers and mathblogging folks. You people are the best!
Oh, and it took me a while to realize that I had actually been on Jekyll before moving to WordPress. Guess that means I'm going back to WordPress in a few years. (@future self: again, very sorry! Let's wait until we hit 9999 posts, ok?) One thing I regret losing is the postspecific history from WordPress; couldn't get that to survive this migration (but will back the database up for myself). Hopefully git will improve this (with some autocommitting).
With Jekyll I switched on some basic CI (thanks, Travis CI!), including htmlproofer. With ~1000 links right now, it's no surprise that some of them are dead. Fixing the internal ones along the way of my review was easy enough. And for the rest (but not that many), I used the Wayback Machine; a handful are actually lost forever.
What was surprising to me was which links needed the Wayback Machine. It's not surprising that some random app on appspot goes down. But something on Harvard.edu or publishers.org? That's somewhat funny (and painful). Small niche blogs? They were solid. You are all awesome!
Being on such a long hiatus (also caused by having other writing projects that bled me out), I want to get back into writing here. Since this site is now a git repo, you can file bugs on the GitHub copy but also fin ideas for posts I put down as issues.
I was thinking about some technical posts on math on the web. And there's one post that's been in the works for months; I should finish that one. Or give it a few more months maybe; you know how these things go.
]]>I always preferred to be the master of my domain. The king of my castle. But literally, not the Seinfeld euphemisms sense. In any case. I've been thinking about a page where I can post short thoughts about math, life and otherwise. The blog is not suitable, since I'm not going to add a post each time I have a new thought. So instead I've started a blurbs page. Each blurb has a number, and an anchored link that you can use in case you want to share it. Continue reading...
]]>If you are not on this list, you better hurry up to this application form and register! Come on, what are you waiting for??? Continue reading...
]]>There is no registration fee, but please register your attendance or obtain any further details by contacting Nick Gill. All events are held in rooms G310 and G311. Morning tea, lunch and afternoon tea are included and complementary. There are limited funds available for dinner — please let us know if you would like to join us.
A list of titles and abstracts for all talks is now available.
09:30  coffee 
10:00 
Session 1: Combinatorics and cryptography</p>

12:00  lunch 
13:30 
Session 2: Numerically modelling the atmosphere</p>

15:30  coffee 
18:00  dinner 
09:30  coffee 
10:00 
Session 3: Operational Research</p>

12:00  lunch 
13:30 
Session 4: Group Theory</p>

15:30  coffee 
18:00  dinner 
The meeting is supported by an LMS Conference grant celebrating new appointments and the University of South Wales.
]]>But without the axiom of choice the world is indeed a strange place. This was posted as answer on math.SE earlier today. Continue reading...
]]>We have verified, in the meantime, that the same person impersonating me on Quora is the one who used Isa's name in those comments. Continue reading...
]]>But if I want to be sure that I can finish next year, I should probably omit one of the problems I originally wanted to solve; and keep that for later, unless it turns out to be particularly simple when I finish the rest. Continue reading...
]]>Mathematics will often dangle in front of you some ideas, and you will work them out, to find a mistake. Then you will go back to the beginning, find new ideas that she had in store, work those out and proceed only to find a mistake much later. Then you go back to the beginning, and you find yet another minor idea that was missing, and now when everything works you continue. But then you find another gap, and you have to go back to the beginning and hope to find yet another idea. And don't get me started on those ideas that you find not to work during all these searches. Continue reading...
]]>Switching back to a static site generator. Jekyll, which took me a while to decide on. In the end, Ian Mulvany rang true. Jekyll is trivial to set up (I'm using Poole/Lanyon), hosting on GitHub pages, some simple CI via Travis).
I thought about exploring other staticsite generators (in particular JSbased ones) but, in the end, Jekyll is the staticsite generator so it's easy to switch to and from if I need to.
I'm not yet going to switch the old site over since I have yet to properly import the older content, set up redirects etc.
]]>What struck me about the conversation was the nature of the discussion. I suppose a good example was a ever so slightly sharp turn in the conversation when it came to the translation of a Lewis Carroll poem which, in its new translation, featured a Porsche  an anachronism that met criticism from the host.
What caught my ear was how these two talked eyetoeye, the host displaying indepth knowledge not only of literature in general but the guest's work in particular. This allowed them to discuss how the writer worked, the real essence of her work, the challenges, the modus operandi. (What also made me wonder was the precarity of the writer; the collection came out of her PhD work, the first book seemed only a success in so far as it landed her some prize/stipend that allowed her to write the second book. Literary careers always sound like scientific research careers, yet we keep things separated.)
I've always yearned for the equivalent of an art critic (which the host evidently provided) but for math and science. One of my first blog posts ever was about mediocrity and, in may ways, critics are the perfect example of why mediocrity is [pun not averted] critical. Instead of pretending to pursue "high" art/science/math a critic is helping their field by providing constructive (and when necessary destructive) review. In public. We do not have this for STEM. Yet the discussion between those two was as esoteric to me as a discussion about forcing axioms or JavaScript libraries would be to them. Of course, German Feuilleton (oh my, I had no idea about contemporary meaning in French) assumes none of its work is esoteric but features 0% of real science criticism (let alone math).
Skip back a few years. My only comment left on Carta.info (no link because I can't find it and because carta has become quite strange) was a foolish, trolllike comment (confirming Hanlon's razor, it was out of stupidity) where I wondered why DLF's Presseschau never included quotes from blogs, since I clearly had (and have) the impression political bloggers are on par with those strange, smalltown newspapers that make it into that selection of op eds. (IIRC, there's now some minor tech segment on DLF that features some blog posts; oh well.)
Over the past year I started to listen to more and more podcasts, primarily about web technology, i.e., work (it all started with the excellent Shoptalkshow). Listening to the conversation on DLF, I realized two things. First, technology podcasts provide just that criticism for web technology. While it's often infantile, it's equally often profoundly useful. As usual, web tech is trying to skip an old medium; a loss for both sides.
Still, during the DLF conversation yesterday I realized that I need to look for another kind of technology podcast: one about actual code. That is, where developers talk about their approach to programming, problem solving, how various tools do their job, and who knows, maybe even actively review code. In other words, a podcast that does for web tech what the DLF piece yesterday might do for writers. Maybe streaming things like twitch.tv (and perhaps livecoding.tv if it ever goes [pun not averted] live) will fill the gap naturally. Still, I'll have to hunt around some time.
Thinking back to mathematics, the podcasts I tried do not fill that gap. There are really good ones out there but they are not on the level of that DLF conversation or on the level of technology podcasts. They always seemed to be more interested in news, puzzles etc rather than challenging the listeners and the experts alike. Which reminds me, I should try to pick up Vilani's book.
Later it smelled like Sommerregen. And everything was well.
]]>It occurred to me today that this is a very Kurtzian story, if we take the Brando interpretation of Mistah Kurtz (he dead) in Apocalypse Now! (the Redux version is one of my favorite movies, I guess). In the movie Harrison Ford plays a tape where Kurtz is describing a snail crawling along the straight edge of a razor, crawling slithering, this is his dream, this is his nightmare. Continue reading...
]]>Yesterday was the first day where you could say that the weather is characteristically spring; and today (as well tomorrow) we are expected for a daytime heatwave and a nighttime cold weather (e.g. BeerSheva is expecting a whopping 31 degrees centigrade during the day, and 13 during the night). Continue reading...
]]>So I am happy that I have only one course each day this semester. I am teaching two courses this semester. Precalculus (Math 200) meets on Tuesdays and Thursdays at 8AM, and Elementary Algebra (Math 96) meets on Mondays and Wednesdays at 9:15 AM. (Each class meets with me a total of five hours per week.) Then on Fridays I have the set theory seminar at 10AM at the Graduate Center, or occasionally a faculty seminar at LaGuardia at 9AM where we will prepare to teach a seminar for first year LaGuardia students. I think that will be cool, because I really enjoyed my first year seminar as an undergraduate student at Grinnell.
This morning schedule is a big change for me; I have been a total night owl for the last seven years at least, rarely getting up much before noon. But I think it will be good for my health to wake up more with the sun. It might be a rough adjustment period, but it will be worthwhile. As a bonus, if all goes well, I can leave work by mid to late afternoon most days and be able to go out in the city some weekday evenings for dinner or a show. (If all doesn’t go well, I’ll be buried in grading, course preparation, administrative work, etc. and rarely get out of here until late anyway. But I am optimistic that it will be better than that.) Another nice benefit to the schedule is that I can conveniently make myself available for 45 minutes worth of office hours four days per week, so that students have a better opportunity to see me.
The elementary algebra students seem like a good group. They really seemed to appreciate the activity of sharing their feelings towards math and their expectations for the course. The videos didn’t seem to be as effective; only a few students commented on them, but the initial discussion before the videos was quite fruitful. A few students told me that they hate math, but many, I think a majority though I didn’t count, came in with positive attitudes towards math. Now it is my responsibility to help them to maintain these positive attitudes and to work hard and succeed in the class. I’m up for the challenge.
]]>For posterity, here's the version I submitted, including typos
Without mathematics, there's nothing you can do. Everything around you is mathematics.
Shakuntala Devi
It has always surprised me a little that the web  created at CERN by a trained physicist turned computer scientist  was born without much consideration for math and science. Of course, it isn't all that surprising since the original HTML lacked more basic things (such as support for tables or images). Either way, people did see the need early on and in 1995 the draft of HTML 3 proposed a <math>
tag, adding basic math support in HTML. Unfortunately, HTML 3 was rejected by browser vendors, and its more fortunate successor, HTML 3.2, dropped the <math>
tag (among other things). As was the fashion of the time, the <math>
tag was turned into a separate XML specification and within a year MathML was born. Problem solved? Not quite.
MathML did turn out to be hugely successful in the XML world. Authoring and conversion tools quickly made MathML easy to create and edit while publishers adopted MathML in their XML workflows. The main reason was that MathML provided a robust, exchangeable, and reusable format for rendering and archiving equational content. However, XML did not succeed as much on the open web and the XML legacy made it difficult to use MathML in HTML itself. This meant that mathematics (and in extension scientific notation) remained a secondclass citizen. Surprisingly, MathML did not simply fade away like other web standards but made a comeback in HTML 5, where we can now use like any other tag. Problem solved? Not quite.
Despite its success, its rich ecosystem, and its importance for research and education, MathML continues to struggle on the most critical front: browser adoption. So far, not a single browser vendor has actively developed their MathML implementation. While Internet Explorer and Chrome lack MathML support entirely, Firefox and Safari at least accepted code contributed by volunteers (and in Mozilla's case actively supported the code base). To compensate, the MathJax project (disclaimer: which I work for) developed an opensource JavaScript solution that authors and publishers can easily drop into their content. MathJax renders MathML on the fly, providing highquality output that works everywhere out of the box, using only web standards such as HTML and CSS. A joint venture of the American Mathematical Society and the Society for Industrial and Applied Mathematics with the support from numerous sponsors, including Wiley, MathJax has become the gold standard for math on the web with our free CDN service alone registering 35 million daily visitors. Problem solved? Not quite.
While we are proud of our accomplishments at MathJax, we know that we can only provide half the solution: native browser support must be the goal. Only native browser support can make MathML universal, helping everyone and allowing people to push the envelope for math and science on the web further. I believe a crucial role lies with publishers. Taking a cue from Forbes, now every publishing company is a web technology company. Not being involved in the development and implementation of web standards is a bit like printing books but not caring about literacy rates  if you build it, they still can't come! When it comes to the development of the web, scientific publishers can become the bridge between authors and standards bodies and they can be instrumental in supporting the development of tools and processes that push everyone forward. Problem solved? Not quite but if you build this...
The reintegration of MathML into HTML5 was a huge step towards math and science becoming first class citizens on the web. MathML is not only a fully accessible exchange format for mathematics but it is also part of other scientific markup such as the Chemistry Markup Language and the Cell Markup Language. The future of MathML in browsers will determine the future of scientific markup on the open web. In the end, a chemical reaction or a data plot has no more reason to be a binary image than an equation  we need markup that is alive in the page and can adapt to the needs of the users. Only this will allow us to develop new forms of expressing scientific thought, forms that are leveraging the full breadth of the open web platform, that are truly native to this amazing medium called the web. And that would be an exciting problem to have.
The comments were also interesting.
Thank you Peter for your accurate and witty post, and thank you for MathJax which has served as a beautiful solution to math on the web. The lack of support from browsers has been pathetic and shameful, and you are right that the only real solution is that MathML (and other MLs) are supported natively supported as the definitive content. We should not really have to resort to "tricks" such as MathJax, however well executed those tricks might might be!
Thanks, Kaveh. As I wrote, Firefox and Safari do have some support for MathML and of course MathJax is also not yet complete in its implementation (there's only so much room in a nontechnical post).
In my humble opinion, it's an achievable goal for a publisher to produce MathML that renders fine on Firefox's native support (while I don't think the same can be said about Safari at this point).
Of course in practice we simply cannot restrict users to browsers these days, so until there is native support of MathML in all popular browsers, we'll continue with MathJax which does work on all. ;)
Here's hoping that one day, we won't have to. Wouldn't that be a nice problem to have?
The best way to get all browsers to support MathML natively is to push math users to use Firefox for its native MathML support. That will get the attention of the other browser vendors. Unfortunately, even in this post you didn't clearly commend Firefox for being the only browser with native MathML.
Thanks for the comment, Robert. I'm not sure who you have in mind with "users". I would agree that authors should ensure that their MathML renders well on Firefox natively.
I wouldn't quite agree to call Gecko/Firefox the only browser with MathML support. WebKit/Safari made a lot of progress last year thanks to Fred Wang's work even if it's behind Firefox in its implementation.
By "users" I mean people producing and viewing math content.
I'm glad Safari is making progress. Feel free to recommend it too. The important thing is to create market pressure for browser vendors to implement native MathML, and that means users/developers choosing one browser over another because of MathML.
As you probably realize, MathJax being so good has actually reduced that pressure; it's easy for browser vendors to say "hey, MathJax works fine in our browser, so why bother investing in native MathML". Even in this post, you haven't clearly identified reasons why native MathML is better than MathJax fallback.
I fully agree that users should choose browsers for their features and Firefox's MathML support is, to me, a huge factor, especially in an educational setting. (In fact, I just recently had an interesting situation where I helped a student struggling with a school project about HTML that required some math  and naturally he chose MathML since they were using Firefox and he wasn't even aware of browser support issues  bliss ;) ).
I've encountered the "MathJax is holding back browser implementations" argument a couple of times now and it feels like a Catch22 to me. Without MathJax (I think) there wouldn't be significant amounts of MathML on the open web and thus no incentive to implement MathML support natively. Now, with MathJax, there's lots of MathML, yet there's still no incentive. I suspect the reasons lie elsewhere. (And from speaking to Gecko, WebKit and Blink developers it does not lie with the developers).
The reason why I didn't go into technical details about why native support is so important is that it didn't fit in this forum (both in length and audience). But you're right that perhaps I should have tried better. Some basic notes can be found on my personal blog at http://boolesrings.org/krautzb...
You and others here say MathJax isn't an adequate solution. But you don't explain why? It seems like a very successful project, and a far better approach from an software engineering perspective than native browser support.
Adding MathML support into every browser requires duplication of development effort and places responsibility for maintenance in the hands of browser vendor employees for whom MathML is neither a priority nor an area of expertise. Each implementation will vary in its performance, bugs and featureset, and authors will need to know these differences in order to produce content that is compatible across all browsers. Future versions of the MathML spec will require development and deployment across all browsers, increasing the cost and delay in making new features available.
In contrast, keeping MathML support within a library allows development to proceed at its own pace, handled by those for whom it is both a priority and an area of expertise, and removes the crossbrowser compatibility burden. MathML users then only have to deal with a single set of features and bugs, and can upgrade to newer versions of the library as and when they need to, instead of being beholden to browser development and upgrade cycles.
It seems like browser vendors would be better off concentrating on providing powerful, general lowlevel APIs for things like parsing, layout and rendering, in order to help the implementation and use of libraries like MathJax. That way, the web can scale to support custom rendering of not just MathML, but also Chemistry ML, Cell ML, and the many other useful markup languages and formats, while reducing the centralisation of effort and complexity within the browsers themselves.
But you don't explain why?
See my other comments on this.
As for the other points your raise, they seem to apply to any newer web standard so I don't quite see how they're relevant to MathML specifically.
But yes, certain lowlevel APIs could make MathML polyfilling much easier; no surprise there. However, their implementation seems even less likely  especially since some of them have been rejected in the past.
Besides, MathML is not rocket science. It adds a few basic constructs to HTML/CSS such as multiscripts, stretchy characters and better table alignments. If you look at Gecko and WebKit it's clear that it's not a huge burden to maintain.
I don't see any concrete technical reasons in any of your other comments for the inadequacy of MathJax. Could you be more specific about which comments you mean?
As for other new web standards, you are absolutely right that same points apply to them. The web has to get away from the situation where features must be implemented natively in the browser in order to avoid feeling secondclass. That is the only way the web will be able to regain competitiveness with native platforms like iOS and Android. As it stands, the web is losing ground quickly to these platforms, because the need to implement features natively results in an unacceptable bottleneck in innovation.
Fortunately, while there may have been resistance in the past to making lowlevel capabilities available to library authors, that is changing. For example, there W3C CSS Working Group has recently created the Houdini Task Force [1] which aims to design lowlevel APIs for parsing, layout, content fragmentation and font metrics. I am certain that they and others would be very interested in hearing what APIs would help in implementing MathJax and equivalent libraries. The Extensible Web Manifesto [2] also covers similar ground.
[1] https://wiki.csshoudini.org/
[2] https://extensiblewebmanifesto...
−
Thanks, I'm well aware of Houdini and the extensible web manifesto and these are great initiatives with excellent people involved (such as Rob who commented here as well).
Personally, I think reports of the imminent death of the web are exaggerated. But even so, I'd argue that abandoning important and established web standards will do nothing but speed that up.
As for the technical issues, they are (again) nothing particular to MathML. Polyfilling a textual rendering component  be it math or bidi or linebreaking  always happens too late in the game, i.e., after the page renders because good layout will depend deeply on the surrounding context. Similarly, inserting large amounts of content fragments (easily in the thousands) into the DOM will always come with issues, especially performance.
More importantly, relying on a polyfill will prevent universal use. Developers will always have to make a conscious decision to add support, adding complexity and risking instability. In reality, we could never expect to be able to use mathematics in something as basic as a webmailer or a social network.
The thing is: the "if" is not even the problem. When you ask actual browser developers (be it Mozilla or Google or Apple or Microsoft) they in favor of MathML. The problem lies much more on the management side.
Ultimately, it comes down to how important mathematics is. (Why not kick bidi? SVG? flexbox? tables?)
The web is the most important medium for human communication and mathematics is one of the oldest and most universal forms of expression. Every school kid (worldwide) engages in mathematics (often for many years) and soon will do so in an HTML context. In particular, students will have to actively communicate (author, share, digest) mathematics and this will primarily happen on the web. To me, that makes it pretty important to have math natively on the web.
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http://www.ctpost.com/news/article/Hereswhyyoushouldstudyalgebra4710461.php
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Here are a few terminological ideas that I doubt are going to be developed by anyone. But if you plan on doing something similar (or if my terminology inspires some proof) feel free to use these terms, and please let me know! Continue reading...
]]>It didn't really work out but perhaps in a good way. Yes, I posted 7 out 8 weeks so that's close (still, Mike gets to name a charity of his choice). No, I most definitely did not spend just 30min per post (more like 1h, sometimes way more...). But those were means to an end which included a) try out something that gets me to write more regularly and b) make it interesting for my two readers, maybe add a third reader (crazy, I know!).
At the end of the year I was exhausted (so I had to take January off  well, be kind enough to pretend I did that intentionally and not simply failed to write that one last post for week 8). In part this was due to me writing on a couple of other, workrelated places. I suppose one could say the blogging challenge helped there; e.g., it motivated me to finish a couple of outstanding blog posts on mathjax.org. But I think in reality it was the holidays and I had enough opportunity to write for a couple of hours (or sleep in to compensate).
As for the means, this exhaustion leaves me in doubt for the first one. Did I simply overdo it? Maybe I just need to pace myself better. We'll see (thanks to Asaf for bugging me to get back on the wagon).
As for the second one, I think that was a bit of a miss. At least in the sense that my posts seemed to cause a lot of confusion and irritation. Then again, that was somewhat intentional, I just wasn't happy with the kind of confusion, perhaps.
As for 2015, I will try to pace myself better. First target: finish that post from the original list of the tiny blogging challenge.
Comments
Last week I wrote about why I care about MathML in general. Given that I work for a project that serves as a MathML polyfill, it's worth while to to point out why native implementations matter; they matter an entire alot of mattering.
A while back, Alex Miłowski asked me for some quotes about how native MathML implementations are important so luckily I can copy myself here.
Some people say, "few people on the web need MathML support." This is true. Just like saying "few people need children's clothing".
Why is MathML important? Education, education, and education. Mathematics is a core skill and a vast amount of educational time and effort is spent on teaching children and adults to understand and apply math & science. Very soon, HTML will be the dominating delivery method for educational content across the world. This means mathematics must be HTML, viz. MathML.
Where should HTML rendering be implemented? In the browser!
MathML has been HTML from its inception and after a (forced) XMLdetour, MathML is back where it belongs: a part of HTML5. MathML layout is core HTML functionality, widely used in everything from web communities to professional publishers to educational startups. HTML and thus MathML rendering belongs in the browser.
While browser vendors show great interest in enabling polyfills to behave like native implementations, polyfills implementing layout standards (MathML, Flexbox etc), in the end, will not achieve native performance. The reason is simple: layout polyfills simply enter too late in the game  after the browser layout is done, at a point where the user expects content, not additional rendering delays. Moore's Law helps a little but, ultimately, performance issues will prevent math and science from fulfilling their potential on the web.
Even the most advanced polyfilling technology will remain a JavaScript solution. This increases the risk of problematic interactions with regular scripts for design, user interaction, and styling. Native support will always be more robust for web developers and consumers.
Even the most ideal polyfill will require a conscious choice of the web developer to load it. This poses a grave restriction for end users and the emergence of new platforms for math and science on the web. From webmailer, to web based authoring, to social networks, all of these could turn out to be highly productive platforms  but it's unlikely their developers will consider adding a polyfill for a perceived niche. With native MathML rendering, rendering MathML would be universal.
The web has revolutionized how we communicate. Not by magic but because thought leaders continually push the envelope, building new tools and platforms that transform how we work, speak, and think. These innovations feed back into standards development, enabling everyone to benefit and restarting the process, pushing us further.
MathML 3 captures traditional mathematical typography. Thanks to polyfills, we get a glimpse of how MathML might develop, how it can revolutionize the communication and dissemination of scientific knowledge. Yet without native implementations of MathML 3, we will never see MathML 4, 5, or 10, and the opportunities this will open up.
It took 50 years from Gutenberg's printing press to the first typeset mathematics book. We're 25 years into the web. Do we wait another 25 years or can browser vendors finally invest 12 developer years to get us there?
Update.
First, I changed the embedded video; it was previously this one.
Second, over on Google+, Harald HancheOlsen asked about the claim that MathML is a huge success. Here's what I responded with.
]]>Re success of MathML. Today, almost all equational content is stored as MathML. This is because almost all scientific (including mathematical) publishers have switched to XML workflows for production and archival where MathML fits in very naturally; similarly most technical writing (e.g., aerospace) is done in XML workflows.
For authoring, it's a bit more complicated. It is similar to, e.g., vector graphics where applications such as Adobe Illustrator have their own formats but when you save vector graphics for reuse you'll most likely export to SVG.
As I mentioned, there's definitely the need for a professionalgrade, open source pure MathML editor (ideally HTML5). The only one I know of is MathFlow. But if you have ever used MathJax then you have authored MathML  it's how MathJax works: convert any input to MathML and then leverage our MathML rendering engine.
Similarly, lots of other tools are able to output MathML  besides converters from TeX (such as LaTeXML or tex4ht), Microsoft Word Equation editor can export to MathML, as does Open Office Math editor, MathType, MathMagic, the Windows Math Input Panel (handwriting recognition), MyScript (ditto), Maple, Mathematica and virtually any other tool you might have authored serious equational content in. (Oh well, I should've simply linked to http://www.w3.org/Math/wiki/Tools#Authoring_tools which I recently set up.)
Of course, Word is the big reason why most scientific and educational content ends up providing MathML. I don't claim (or believe) that people are aware of most of this which was one of the reasons I wrote about it.
When I started this writing challenge, I had listed a couple of potential blog post titles. One of them was "Why you should care about MathML". I realized later that I really didn't want to pretend I could even try to tell my two readers what they should or should not care about. Instead, I want to jot down (remember: 30mins time limt) a few reasons why I started to care about MathML, alot.
Unsurprisingly, it was in many ways a story of my education. Here are two quotes from yours truly.
I think MathML is so far the best solution to present mathematical content on the web
 actually me, Dec. 2009
Actually, more stuff wrong on my post; also, referencing Terry Tao's blog, weird.
But mathml sucks [...]
 also actually me, Feb. 2011
(In my defence, I probably meant authoring tools and browser support.)
So as you can see, I flipflopped a bit there (and, in a fundamentally different way, I still do). So here are five short reasons why I care about MathML.
When I started using MathJax on a personal blog (thanks to the above quote I realize I started blogging 5 years ago this month, (local copy), although I think I started to blog a year ealier on scivee.tv (though this seems lost)), I was first annoyed and then very happy to not use macros. Obviously, you can use macros with MathJax but I started to avoid personalized macros at all costs. Ultimately, they prevented me from writing mathematics elsewhere and they limited reuse of my writing by other people (well, ok, that's more hope than reality I suppose).
MathML does not suffer any of these complications (well, technically Content MathML could if anyone used it). Instead, MathML provides a truly stable format for storing equational content while still allowing for reuse. Granted, it's not exactly easy to write by hand but neither are SVG or HTML/CSS (certainly not as soon as you want to express something more complex). Still, I'd encourage anyone to spend some time with it (e.g., try copyediting a random piece of MathML and compare that to copyediting some macrofilled LaTeX horror). In any case, creating MathML is straight forward, especially for those knowing LaTeX syntax (even if we could use a a good opensource MathML editor). Ultimately, MathML is more readable in isolation thanks to its nature of being actually a markup language and not a programming language.
What struck me early on was how successful MathML was outside of research. Research mathematicians (and scientists) tend to think their habits are vital for the longevity of mathematical writing. However, technical writing (such as industrial (think aerospace) documentation), engineering, and most importantly schoollevel mathematics are arguably more important  and have benefited enormously from a mathematical markup that is easily handled by researchers and nonresearchers alike. MathML has brought high quality rendering together with easy authoring to an incredibly wide and diverse community; a huge accomplishment.
What I also learned early on (in crass contrast to my 2009 self above) was that MathML has turned out to be critical for having truly accessible mathematics.
Of course, TV Raman's AsTeR voiced TeX/LaTeX long before MathPlayer, ChromeVox or VoiceOver voiced MathML. But besides the refinements (which later tools could so easily provide), the notion of accessibility stretches far beyond voicing and visually impaired users. Features like synchronized highlighting would be much harder in TeX (just think about identifying subexpressions in a complex TeX macro, let alone in poorly authored TeX) but they are critical for helping people with learning or physical disabilities. Even more advanced features like summarization and semantic analysis are much more straight forward in a markup language like MathML than in TeX. And so is search whose importance can hardly be overstated in times of ever increasing publication pressure; without search mathematical knowledge won't be accessible to us in the long run.
The main reason why MathML is irreplaceable on the web is its compatibility with the DOM. This allows web developers to apply the full breadth of their tools to make mathematical content truly native instead of copying printbased layout. We cannot reinvent everything as Knuth did because web "typography" is far from finished and communicating on the web will probably change drastically every couple of years for the foreseeable future (just like communicating using the printing press did in another age). Having a naturally fitting technology allows mathematics to continually evolve its expression alongside other forms of expression on the web  an incredible benefit (and challenge!).
This leads me straight to the last and probably main reason why I care for MathML. What the web has already done for regular language (all over the world), it can do for the language of mathematics: transform the way we communicate; expand, enhance, deepen, and lighten the way we express mathematical thought. You don't have to be Bret Victor to believe that in 30 years we will have developed new forms of expressions that truly leverage web technology and eliminate baroque limitations of blackandwhite, print layout. We should strive to do so much better and I believe MathML is an important step in this direction.
]]>Today I only have ~15 min. This week, I happen to be in Chicago for dotAstronomy 6. This might be odd since I'm not an astronomer (nowhere near in fact). It is actually an immense privilege, though, since I'm part of a small group of invited interdisciplinary participants (also including biologists, climate scientists and library scientists). So my perspective is that of an outsider and I hate to admit it: it's what I suspected all along.
That is, ever since running into the dotAstronomy website a few years ago, I have been a little envious. I kept thinking "This sounds incredibly fantastic. How could we do something like this for mathematics?" Until today I could at least pretend that it couldn't actually be as great as it appears. Because nothing is, right?
My two readers won't be surprised to hear it: I was wrong. dotAstro is every bit as exciting, enlightening, creative, and savvy as I had hoped. A fantastic group of scientists from all walks of scientific life, including "recovering" researchers who have been led to nonstandard careers while retaining a deep, nay fierce enthusiasm for their field as well as for the untapped potential offered to scientific communities by the web. This first day has been a perfect mix, starting with excellent talks, switching to amazing lightning talks, followed by an exhaustingbecauseengaging unconference sessions, and finally some great conversation at the pub (including perfectly greasy US bar food).
Luckily, I don't have to bore you with my notes but can simply point you to the liveblogging of the first day by @vrooje. In case my notes go up in flames, I could probably reconstruct half of it from the Twitter hashtags of the unconference sessions I attended, i.e.,
Now I'm exhausted but excited for tomorrow's hack day.
Comments
As you know, this blogging challenge of mine is based on the observation that I would like to write more. And then Jeff Atwood reminds me in this interesting piece that
we badly need to incentivize listening
which makes me wonder if my natural tendency to let things brew for ages might not be a good thing. This blogging challenge will invariably show if I'm actually able to write in decent quality under tighter constraints. (Right now, I'm not so sure.) So perhaps I will have to realize that silence is golden.
On a related note, in recent months, I was forced to think about my comment "policy". This hadn't really come up before since I get very few comments and even fewer from strangers. But I think I should point out that nobody leaving a comment should expect said comment to be posted. Similary, nobody should expect a comment that has been posted to stay up (especially if gets posted automatically after I've allowed a comment in the past). Finally, nobody should expect me to reply to a comment even if I've replied to other comments and even if that happened in the same thread.
This policy has very little to do with trolling, actually, but more with offtopic comments and comments on ancient posts documenting how things have changed (I'm so surprised! not). It's also related to a different point: I'm probably switching off automated comments at some point next year (ooooooh, something will change, hint hint).
The number of worthwhile comments I get is roughly 1 per month (vs 510K of spam). So instead of a comment sytem, I'll figure out some way you can quickly send me a comment and then I will add it manually. This move is not just laziness about dealing with spam (it will be slightly more work, I suspect) but also reflects the fact that I consider your comments to be additions to the content, not separate from it. This does not mean that a comment needs to be serious, of course  silly comments are just as (more?) (more!) relevant to me, so I hope people will keep'em coming.
Comments
Darth Vader/Stewie: Oh, come on, Luke, come join the Dark Side! It's really cool!
Luke/Chris: Well I don't know. Whose on it?
Darth Vader/Stewie: Well um... there's me, the Emperor, this guy Scott. You'll like him, he's awesome...
Where my previous post was more about TeXlike syntax, this is about TeX/LaTeX proper. If you're a TeX/LaTeX enthusiast, don't go all crazy on me (I mean, have you seen my thesis?). This is about me feeling a growing awkwardness towards TeX/LaTeX. And this has little to do with TeX/LaTeX itself.
TeX/LaTeX is a tool. It is a tool designed by Knuth to solve a problem in print layout. The trouble is: print is becoming less and less relevant and I think this holds for most TeX users (when was the last time you went to a library to look at the printed copy of a current journal issue?). What is not obsolete is PDF and TeX is, of course, very good when it comes to generating PDF.
However, this "Portable Document Format" is really quite useless in the one place where people consume more and more information: the web. (I admit I'm of the conviction that the web won't go away; crazy talk, I know.) And for the web, TeX/LaTeX is the wrong tool. Yes, there are about a gazillion projects out there that try to bridge that gap, try to create HTML out of LaTeX. But if you try them out you'll soon notice that you'll have to restrict yourself quite a bit to make conversion work.
Turn this around and you'll realize that the community as whole has a serious problem: almost nobody writes TeX/LaTeX that way which means almost all TeX/LaTeX will never convert to web formats well. To put it differently, there's a reason for a large market of blackbox vendors that specialize in TeX to XML/HTML conversion for professional publishers (and this often involves rekeying).
This is, of course, in no way a fault of TeX/LaTeX itself which was designed for print, in 1978. But it is a problem we are facing today.
Now TeX is Turing complete and this means we can do everything with TeX (even toast). So a universal output for the web is theoretically possible. However, everything is nothing if we can't make it practical. Perhaps one day, we'll be lucky to find another Leslie Lamport who will give us "HTMLTeX", i.e., a set of macros that work and rapidly become the defacto standard for authors. I doubt it. (And not just because I know mathematicians who don't upload to the arXiv because their ancient TeX template won't compile there.)
I doubt it because there's no problem to solve here. Where Knuth (and Lamport) solved imminent problems, there is no problem when it comes to authoring for the web  a gazillion tools do it, on every level of professionalism. TeX is neither needed for this nor does it help.
"The best minds of my generation are thinking about how to write TeX packages."
 not Jeff Hammerbacher.
Another part of my awkwardness towards TeX/LaTeX these days lies in the resources the community invests in it. It feels like every day, my filter bubble gives me a new post about somebody teaching their students LaTeX. These make me wonder. How many students will need LaTeX after leaving academia? How many would benefit from learning how to author for the web?
And then there's actual development. How many packages on CTAN are younger than 1/2/5 years? How many of those imitate the web by using computational software in the background or proprietary features such as JSinPDF (and who on earth writes a package like that)?
To me, this seems like an unfortunate waste of resources because we need people to move the web forward. If we remain stuck in PDFfirst LaTeXland, we miss a chance to create a web where math & science are first class citizens, not just by name but by technology and adoption from its community.
If only a part of the TeX/LaTeX community would spend an effort on web technologies like IPython Notebook, BioJS (or even MathJax) it would make a huge impact.
This brings me to my last awkward feeling about LaTeX for today which comes on strongly whenever somebody points out that LaTeX output is typographically superior.
I understand why somebody would say it but once again LaTeX is a merely tool. The reality of publishing is that almost all LaTeX documents are poorly authored, leading to poor typesetting. In addition, actual typographers will easily point out that good typography is not limited to Knuth's preferences enshrined in TeX.
So while I can understand why somebody would claim that their documents are well typeset, this is not very relevant. As long as we cannot enforce good practices (let alone best ones), the body of TeX/LaTeX documents will remain a barely usable mess (for anything but PDF generation).
On the other hand, publishers demonstrate every day that you can create beautiful print rendering out of XML workflows, no matter if you give them TeX or MS Word documents. Even MS Word has made huge progress in terms of rendering quality and nowadays ships with a very neat math input language, very decent handwriting recognition and other useful tools.
The web is typographically different. On the one hand, much of its standards (let alone browser implementations) is not on the level of established print practices. On the other hand, its typographic needs are very different from print for many reasons (reflow, reading on screens etc). And even though some of print's advantages will eventually be integrated, I suspect we will develop a different form of communication for STEM content on the web than we have in print because we have a much more powerful platform.
Comments
\label{...}
in the 4th example, and then \ref{...}
that label in Section 4. This would also improve the PDF by allowing a link to the reference.\newcommand
is available, but its definitions must fully resolve in the vocabulary of the profile. The language of the profile should be sensible both for classical print and for HTML5. See my talk at the TUG meeting in 2010, http://www.albany.edu/~hammond/presentations/Tug2010/LaTeX is the path to the dark side. LaTeX leads to TeX. TeX leads to DVI. DVI leads to suffering.
 not Yoda.
Ever since joining MathJax, MathML has been a major part of my professional life. It's a slightly unhealthy relationship: wideeyed enthusiasm and bottomless despair are frequent companions (although, I think, I'm becoming slightly more stable). Among the web standards of the W3C, MathML is, I think, unique and this is both good and bad (and topic for another post).
One thing that comes up regularly in discussions is how the use of LaTeX notation on the web is somehow evil. I believe this is a phantom menace.
You might say that comparing full TeX/LaTeX and MathML is comparing apples and orange  at most, I should be comparing mathmode TeX/LaTeX to MathML. But the problem is that the difference is tricky since mixing math and tex mode is all too common in the real world. Since TeX is a programming language and lacks enforceable best practices, there will never be a "good" subset of TeX/LaTeX that could provide reasonable markup constraints. The reality of how people use TeX/LaTeX is just too messy.
Quite literally, there is no such thing as "LaTeX" on the web. What is really being compared is a bunch of TeXlike input languages. If you think Markdown is bad off (yay CommonMark!) take a look at the number of easily incompatible TeXlike input on the web. MathJax's TeXinput vs Wikipedia's texvc vs iTeXMML vs pandoc vs ...  they are all different on some level.
And even if you think: oh well, one day there'll be one standard LaTeX subset for the web (right?), then there's still no threat here. Markdown, wikitext etc have never threatened HTML; raphaeljs, d3.js etc have never threatened SVG; threejs, pixi.js etc have never threatened WebGL. Instead, these tools pushed the use and thereby the standards forward. Pretending that TeXlike input (or asciimath or jqmath) has any other affect is a phantom.
While you might still wish to speculate that LaTeX could somehow be coaxed into being playing nice with HTML, CSS etc, the story really ends at the DOM. LaTeX does not fit in the DOM; period.
There is a reason why MathML is so damn good for mathematics  it was created by people with a huge amount of experience, in particular in TeX and CAS. So in many ways, MathML is the natural continuation of the insights gained from TeX, applied to the web.
While at first sight MathML appears verbose (just like HTML or SVG might appear), it ultimately has one huge advantage over TeX: it is clean, selfcontained, and stable. MathML provides a clearcut presentation of equational content. It is infinitely easier to understand someone else's MathML than it is to understand someone else's TeX. (And you also cannot redefine \relax
in MathML...)
Fun fact: for roughly a decade, almost all new mathematics has been stored as MathML. Mathematicians are usually surprised by this  doesn't every math journal accept TeX submissions? That's true and nobody would claim that the majority of mathematics is authored in MathML (come to think of it, that one probably goes to MS Word). But unless you publish with a very mathspecific publisher (e.g., the AMS), your content is invariably converted into XML and your equational content into MathML. So even in pure math research (which is a miniscule amount of mathematics published compared to STEM in general) the authoritative format is MathML.
So LaTeX as a web standard is just not practical. Which brings me to my final point. If MathML fails because of a bunch mathmode LaTeXlike input thingies, then I think we deserve to fail. These are such a weak contender, MathML would have to be truly a miserable standard to loose out. By contraposition, the fact that MathML is far from miserable (as its success demonstrates every day) means it will not fail no matter how many web pages include TeX/LaTeX in their HTML.
The more interesting question for me is where this phantom originates from. I suspect this is really about the lack of browser implementations. It's always easier to look for a scapegoat. Making up a phantom like TeX will distract us from the important discussion: what's really holding back browser implementation? It's definitely not the math end where MathML simply rocks. And then the really interesting question can be: what could MathML 4 and MathML 5 look like?
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25 years ago today, the wall fell in Berlin, opening up Germany, opening up Europe. Admittedly, I don't remember much about that night; of course, I technically remember (and reconstructive memory is grand) but the event held little signficance to 10yearold me. (Though arguably not zero signficance since I had actually visited Berlin for the first time that year, and I remember standing on a platform near the Brandenburger Tor, looking over the death strip to that iconic land mark and not really understanding things).
As you may have noticed, I recently moved back to Germany and most recently to Göttingen. This meant, after some 8+ years, I'm living in West Germany again. Admittedly, when I lived in Berlin while working on my PhD, I lived in a heavily gentrified (i.e., Westernized) East Berlin quarter (fun fact 1: at the time, the percentage of foreign citizens in Prenzlauer Berg was precisely the city average, with the "slight" difference of almost all of those being from G8 countries...). Still, even that part of East Berlin (let alone other parts) remained structurally very different from, e.g., Bonn and Munich. A particular aspect for me was always the absence of the typical West German "infrastructure" of small shops and businesses (or ATMs for that matter). In any case, Prenzlberg still felt incredibly different from anything West German (though not as much as it did in the 90s or even early 2000s when I first fell in love with Berlin).
It has struck me how Göttingen, to me, seems like a perfect example of a West German city. I can't quite pinpoint this particular feeling. Maybe it is the beautiful 18th century city center (fun fact 2: supposedly Laplace urged Napoleon to spare Göttingen because Gauss might get hurt), maybe the lovely ring of late 19th century quarters surrounding it, perhaps the 50s Karstadt, the 70s Neues Rathaus, and the 90s malls. Certainly all of that a little. The city has also seen the typical postWWII redesign towards cars as primary mobility solutions, which makes it a mess for the large number of bikes, pushing them to the sidewalks to collide with pedestrians (fun fact 3: I couldn't remember when I had last seen an atomkraftneindanke flag but I did see one on my first trip to Göttingen). Göttingen has this feel of wealthybutreluctanttoadmitit (as so much of West Germany). It's filled with students making it appear modern and young and yet it's history weighs heavily in places (bizarro Bismarck adoration in the Bismarckturm does not compute). Göttingen is also surrounded by a beautiful countryside with a gazillion potential destinations for the weekend, many having been popular retreats at some point of the city's long history. Of course, for a mathematician, Göttingen is a particular attraction and yet it's hard to ignore the great purge in 1933.
Göttingen has this particular, everythingisfinished vibe (with a noroomforchange beat) which I find so typical of West German cities. It's oddly appealing (especially after returning from SoCal) and yet slightly suffocating. If you want to live in a perfect example of West Germany, come stay in Göttingen. At the very least, you can stop by Gauss's grave and since it's a 5 minute walk from my home I expect you to stop by for a coffee after.
Today, celebrations of the peaceful revolution of 1989 may be in focus. But on November 9 we always remember more. 1918, 1923, 1938, 1989; I can't remember one without the other.
]]>Still, I miss writing. So I'm setting myself a tiny blogging challenge for the few weeks remaining in 2014.
Yes. I don't want to take on a 1postaday challenge because, well, I'd simply fail. I'm no Cathy O'Neill. So most likely I'll write these posts on the weekend or possibly late at night.
One post per week seems reasonable. It's realistic, I've done it in the past yet it's far from what I'm currently able to do.
Not a lot, I admit, but the averaging napping time of certain person. Given that my usual writing includes a procrastination phase of 56 months I'm expecting a change in quality. I'm just hoping for an improvement, given that more writing regularly should mean more practice.
I thought it might be prudent to have a couple of topics ready so that when I sit down (not unlikely on a Sunday at 11:30pm to make the deadline) I have a last resort for a topic to babble about.
Note that these are not actually related to drafts or even proper ideas. They are just ideas I jotted down over the past few weeks.
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And it seems my new neighborhood is trying to tell me something.
Oh well. I supposes that's what you get for moving to the town where these folks spent very productive years.
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Definition. Let \(V\) be a model of \(\ZFC\), and \(\PP\in V\) be a notion of forcing. We say that a cardinal \(\kappa\) is "colloopsed" by \(\PP\) (to \(\mu\)) if every \(V\)generic filter \(G\) adds a bijection from \(\mu\) onto \(\kappa\), but there is an intermediate \(N\subseteq V[G]\) satisfying \(\ZF\) in which there is no such bijection, but there is one for each \(\lambda\lt\kappa\). Continue reading...
]]>In case you forgot, \(\kappa\) is a huge cardinal if there is an elementary embedding \(j\colon V\to M\), where \(M\) is a transitive class containing all the ordinals, with \(\kappa\) critical, and \(M\) is closed under sequences of length \(j(\kappa)\). Continue reading...
]]>People often like to cite the paradoxical decomposition of the unit sphere given by BanachTarski. "Yes, it doesn't make any sense, therefore the axiom of choice needs to be omitted". Continue reading...
]]>But we can clearly see some various degrees of largeness by how much structure the existence of the cardinal imposes. Inaccessible cardinals prove there is a model for secondorder \(\ZFC\), and Ramsey cardinals imply \(V\neq L\). Strongly compact cardinals even imply that \(\forall A(V\neq L[A])\). Continue reading...
]]>Forcing is horrible. If you can think about it, you can encode it into generic objects. If you can't think about it, you can encode it into generic objects. If you think that you can't encode it into generic objects, then you are probably wrong, and you can still encode it into generic objects. Continue reading...
]]>As you can see, that text file has some beautiful asciiart mathematics. Of course, Doug wanted to code this up properly for the web which means using MathML and the question was: what's the easiest way to do so?
It's not hard to see why I suggested ASCIIMathML (or asciimath). Asciimath was written by Peter Jipsen with whom I happen to have two lucky personal connections  first, I luckily shared a room with Peter at BLAST 2010 (way before I got involved with MathJax, see these posts), second I was lucky enough to enjoy his hospitality a couple of times while we lived in LA, including Peter taking me surfing for the first time in my life  good times.
If I remember correctly, asciimath was born out of pure necessity  finding a way for college students to write mathematics on the web. These kids were accustomed to graphing calculator style input, and Peter, of course, believed that MathML was the right way for an output on the web  so in 2004 he started to write this beautiful JavaScript library to convert from one to the other.
Later on, David Lippman wrote a nice MathJax addon, which was ultimately rewritten by David Cervone, and so nowadays you can use asciimathml in any browser by combining it with MathJax.
First off, if you know some TeX I would probably describe asciimath as "TeX without backslashes". Because, really, why not write alpha
or phi
for %alpha, phi%? Similarly, why not just write sin
for %sin%? (Oh, and let's have a fun discussion about phi
vs varphi
, Unicode vs TeX. But not a problem, you can switch to whichever convention you like using MathJax.)
Second, if you know markdown, then I might describe asciimath as "markdown for math". It's not TeX in all its (infamous) glory or even MathJax's TeXlike input with its many advantages for the web. It's much more restricted and that's by design  much like markdown is.
Given its target (MathML) and its general webbiness, asciimath works smoothly with Unicode, which adds to its readability and usability (and internationalization). Everyone will probably appreciate that >
and →
work interchangeably (both of which seem much saner to me than anything LaTeX would suggest). So f: A > B
and f: A → B
produce identical MathML: %f: A > B% and %f: A → B%.
Similarly, asciimath's minimal approach does not need TeX's cumbersome \begin{} \end{}
environments, but many important tools are available in much simpler ascii/computing notation, e.g., ((a,b),(c,d))
for matrices: %((a,b),(c,d))%.
Personally, I think asciimath probably deserves the title "markdown for math" although I think the title will go to TeXlike input after all (but that's another post).
What I'd really love to see is more people pushing asciimath further. The official ASCIIMathML repository is now hosted on MathJax's GitHub account and we even grabbed a nice domain at www.asciimath.org to have an open page using Github pages for people to easily contribute enhancements to.
There's a lot of low hanging fruit in the form of improving the quality of the MathML (e.g., a\\b
should probably produce <mfrac bevelled="true"><mi>a</mi><mi>b</mi></mfrac>
instead of the problematic <mi>a</mi><mo>/</mo><mi>b</mi>
) and of course asciimath by design should probably not strive to be feature complete (i.e., generate any kind of MathML) which means there should be situations where asciimath will simply fail and, much like markdown with HTML, it could perhaps gracefully mix MathML and asciimath.
But in any case, it's great to have this alternative to TeXlike inputs because TeX is ultimately holding math on the web back (but that's another post, for another time).
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\begin{align} \end{align}
like environements is also a downside of ASCIIMath. I use align environments all the time. I agree that ASCIIMathML aim shouldn't be to be feature complete. But I do think it should be able to generate 90 percent of what a mathematician uses. In other words 90 percent of what is used at math.stackexchange for example.\(W^{3\beta}_{\delta_1\rho_1\sigma_2}\)
W_(delta_1rho_1sigma_2)^(3beta}
W_δ₁₂ρ₁σ₁^3β
(W_δ₁₂ρ₁σ₁^3β)
in this comment box, was allmost trivial using that tool (which can be used as a bookmarklet script).I think there is a world market for maybe five browsers
 not Thomas J. Watson
As my one two regular readers know, I work for a project that's all about crossbrowser support. It might, therefore, not come as a surprise that I use three browsers when working. That's mostly because I love incognitomodes; not just for the slightly increased privacy beyond ghostery/disconnect/abp but for the convenience of a clean, nowhereloggedin browsing experience. However, a sense of realism forces me out of incognitomode, so I spread things out.
On the desktop, I use Chrome for all Googly things (email, docs etc) and all social things (social networks, feed readers etc), Firefox (in privacy mode) for work things (Github etc) , and Chromium (in incognito mode) for other things (aka bouncing around the intertubez). I guess I also sometimes use "Web" (the Gnome browser; weird name) because it's WebKit and every so often I spin up one of Microsoft's testing VMs for IE. On my Android devices I use Chrome and Firefox mobile (I tried Opera and Dolphin as well but never felt like switching). "Manual" browsing I usually do in Chrome incognito tabs, links from other apps get opened in Firefox (because, trust). Maybe I should add the Wikipediabeta app (which is so much better now) but I'm lucky to be on KitKat on all devices (no more horroriblyancientWebKit in apps) so browserwise, I'm ok. And I feel the need to mention duckduckgo which is simply awesome (w00t! I just found out there's Android app. Gotta try that.)
But then there's an iPad in my home (where I'm only a guest). And of course, there are no choices for browsers: Safari is all you get. (In case you didn't know it already, all browsers on iOS have to use the underlying mobile Safari as a rendering engine because Apple's TOS forbid all browser engines in the app store). I think this needs to change.
Somebody recently pointed out to me that after the convergence following the browser wars, we seem to be in a phase of (massive) divergence. And it's not going too well. Browser vendors are doing crazy stuff all over the place. Chrome gets a lot of heat (pulling MathML, CSS regions, threatening XSLT), though I find myself defending them more often than not because they are, at least, transparent (and they're also doing cool stuff like the earliest web components implementation, the CSS font loading API, the (failed) WebIntents etc). IE is like Chrome, just without the positive transparency. How crazy is it to read over at Murray Sargent's blog that IE is using a MathMLcapable rendering system yet MathML is "not planned" in the IE dashboard? Then there's Apple which does things like happily touting MathML support when a) it's still enormously limited and b) it was all done by 34 volunteers (not together, mind you, all fighting by themselves, one following when the other burned out); or using the (nonstandard) Pages engine in iBooks (only for iBooks Author books but still a heck of a bad practice).
Don't get me wrong, fundamentally, I think that's ok  divergence needs to follow convergence. But I think it might take the same level of regulation that we saw in the browser wars to ensure we'll see convergence again. Currently, browsers are more like utilities, yet essentially unregulated. While desktop statistics are slightly better (but not actually good), mobile is an alarming monopoly. Safari on iOS, Chrome on Android; that's it. Sure, you can get Firefox for Android etc. but those browsers are at a massive disadvantage. Back in the day, Microsoft was forced to actively help users to install nonIE browsers (well, in the EU at least). The same should be done for all OSs, including mobile, and possibly even more in terms of apps/webview etc. (Granted, for FirefoxOS, this seems impossible; but just because Mozilla is mostly a positive force doesn't mean they can get a free pass.)
In the long run, I think, we need browsers to become commodities. For this they need to become easy to develop, to modify and recombine  and with regulations to prevent abuse like we saw on Windows and we see on iOS. We need hundreds, maybe thousands of browsers, dozens of layout engines, modular, recombinable etc. I would love to be able to "compile" my own browser  take some MathML support from one place, CSS modules from another, accessibility features from a third etc. pp. Not in the daysgoneby XMLdreams of modularization but in the "hey, codeforkids teaches you to write an HTML9 layout engine" or in a breachbutforreal way (i.e., not just on top of Chromium), or (let's go crazy) write an HTML rendering engine in TeX or lolcode (what's the difference, really?).
Really, there simply has to be room for more than 5 browsers in the world.
PS: Yes, this is mostly about "layout engines", not "browsers". To most people the distinction is meaningless.
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Materiales:
En adición de esta página hay una otra página en Moodle con material de ayuda para esta curso. La página se llama Ayuda Algebra Lineal y está en la sección de Matemática aplicada de la escuela de matemática. La clave para matricularse es Ayuda2014 y solo la deben usar los estudiantes la primera vez que se matriculen.
Si tiene más preguntas, se puede
Well, of course that the answer is negative. If \(\cal U\) is a free ultrafilter on \(\omega\) then \(\{X\subseteq\mathcal P(\omega)\mid X\cap\omega\in\cal U\}\) is a free ultrafilter on \(\mathcal P(\omega)\). But that doesn't mean that the question should be trivialized. What Yair asked was actually slightly subtler than that: is it consistent that there are free ultrafilters on \(\omega\), but no uniform ultrafilters on the real numbers? Continue reading...
]]>Neil deGrasse Tyson pushed a lot on the point that we really push the planet to its limits, and we might be close to the point of no return from which there is only a terrible Venuslike fate to this planet. And that is an important issue, no doubt. Continue reading...
]]>Almost always, the problems are easy to track down (e.g., the infamous 15s delay if a custom configuration/extension/etc has an incorrect loadComplete
call), sometimes they are bugs (e.g., the recent Chrome/WebKit webfont loading bug), but of course every so often they hit on the subtleties that make what MathJax does so hard (ex/em matching, webfont detection etc.).
A surprising recent example for the latter revolves around the use of display:none
. It usually comes up in reports of broken layout but the other day there was an interesting performance issue. To understand the second, it helps to understand the first.
display:none
The rendering issues sometimes seen for content which starts off with CSS display:none
and later made visible stem from a simple problem: browser engines won't actually layout elements with display:none
. MathJax on the other hand, needs to take a few vital measurements (basically widths and heights) to produce a correct layout  and these measurements are not available when the content wasn't laid out by the browser.
To work around this predicament, we could just leave it to the author to work as if content with display:none
was dynamically loaded content  and force them to trigger a manual typeset when the content is revealed. But that's silly because the content is there, we should damn well use it.
So to work around display:none
, MathJax does something quite simple: it moves the content into an invisible element that does get laid out  using visibility:hidden
with zero dimensions. Then MathJax can take the measurements, produce good rendering and put the rendered output back to the original location.
Now there's an obvious problem with that approach: where would you move the content to do the rendering? After all, just because something is display:none
doesn't mean it has no context. It might be in a completely different CSS context (think: hints to a homework problem, sidebar content, menus), or the context might change once it becomes visible (think: popup footnotes/references, knowls). In other words, MathJax output in some other context might get screwed up when put back into the original context (e.g., matching font sizes correctly, dealing with inherited CSS). Of course, more often than not, this will work well but it is a general problem and should be avoided.
(Another way might be to use mutation observers. Besides supported being limited, I think there's an argument to be made that layout should happen right away if possible. But it should probably become an option via an extension.)
Recently, we saw a sample where all this magic had a very different side effect: serious performance issues. In that sample, hundreds of equations were hidden away with display:none
. This meant that MathJax had to shift those around in the DOM  and especially mobile browsers did not like that at all. What made matters worse was that the MathJax status messages gave no useful indication of what was going on, instead hanging at unrelated points  because MathJax currently doesn't have a signal to catch a delay for such a "simple" action like laying out display:none
. In the end, the sample (with 2000+ equations) left the user with the impression that their mobile browsers were hanging/crashing  just because of all these necessary layout shenanigans! Darn!
The moral of the story is: use visibility:hidden
, e.g., position: absolute; top: 0, left:0; width:0, height:0, overflow: hidden; visibility: hidden;
), or tell MathJax to skip the content and manually queue a typesetting call when you reveal hidden content. If you want to put in some extra work, use visibility:hidden
, let MathJax skip the hidden content and then queue a typesetting call for the hidden content after MathJax is loaded; that way the hidden content will be typeset only after the visible content is done (on MathJax's initial pass).
Any which way, don't get caught in bad layout or performance issues related to display:none
!
And so I'm honored to join the unsecret society of Carnival of Mathematics hosts. Indeed, the list of former and future hosts over at The Aperiodical (who took over the organizational stress two years ago, stepping into the tremendously large footsteps of Mike Croucher of Walking Randomly), this list reads like a whoiswho of true math bloggers (the kind that cares for blogging as a community and art form). If you're not on it, do yourself a favor and volunteer right now. I'll wait. Honestly, I will. This post will still be here when you get back; I promise.
In the timehonored tradition, let us remember that 111 has many marvellous properties. However, if I were forced to name a favorite, I could not decide between the fact that the smallest magic square containing 1 and otherwise prime numbers, has a magical constant of 111, as well as the simple beauty of being a palindromic number.
When you enter our attractions, you are almost unnaturally drawn to an oldiebutgoldie, an attraction worth a visit every time the carnival is in town: John Baez's Beauty of Roots. As with Vincent Pantaloni (@panlepan) put it: "The best math I stumbled upon this month is this visualisation of polynonmial roots".
Then stop by Antonio Sanchez Chinchon since he shares with us his mnemoneitoR, to translate numbers into easytoremember phrases inspired by books to generate funny mnemonic rules.
But don't stop there, wonders await as AP Goucher gives us the elliptic curve calculator, a fixed page paper slide rule using elliptic curves.
And while you take a break, make sure to sit down and listen in on Alexandre Borovik's Math under the Microscope pointing us to this New York Times article on a simple onetime exercise that might prevent community college students from dropping out of math classes.
But throw yourself back into the crowds of the carnival because when Colin Beveridge (of Flying Colours Math) was asked why he loves math, he wrote a short and sweet post to make his answer public. As luck will have it, a student asked Stephen Cavadino of cavmaths the very same, and so we can enjoy another answer that might inspire future students to grow their own and personal passion for mathematics.
By now you're hungry and rightfully so. However, if you ever wondered where to place a hot dog stand, and how to adapt when the best customer moves into a motorhome, then fear not  David Orden at Mapping Ignorance will fill your stomach with a great post, taking you from Sylvester's original question back in 1857 all the way to today's cutting edge research.
With a full belly, let's head over to the Aperiodical, where Paul Taylor tackled the mindbending and subtle hidden maths of the Eurovision song contest while Katie Steckles provides us with a recap of Matt Parker's appearance on the BBC's consumer moanfest, Watchdog, where Matt helped everyone get their percentages right.
And while you leave, why not trust him when the Aperiodical's Christian Perfect points you in the direction of Nick Berry's excellent blog DataGenetics, with a post that will introduce you to the wonders of Amidakuji, bringing together braid theory and a very old arcade game.
Then go on and follow Katie Steckle to visit Goading the IT geek's post on the deceivingly simple problem of calculating averages.
And if you find yourself in a part of the Carnival you have already visited, why not take a chance and run into Stephen Cavadino's posts on mathematics on children's playgrounds and small puzzle on the number 71?
Back on the main road through the carnival, you'll see in the far end Alex's adventures in numberland, where Alex Bellos has learned from Joseph Mazur how surprisingly new mathematical notation is.
And if you like to gamble, dear friend, worry not. The BBC's Janet Ball can tell you a story that might encourage you, how the (in)famous MIT blackjack team won enormous amounts of money tackling the odds with their mathematical prowess.
Behold, the Mechanical Turk is nothing against our next mindbending adventure as Andrea Hawksley takes you on a dive into NonEuclidean Chess!
After his shocker, cool down a little and enjoy the talented Shecky Riemann sharing with us his interview with passionate mathed blogger Fawn Nguyen.
Nest step into the ghost house at Google+, where Richard Green took everyone on a journey from simply squaring prime numbers to monsters and moonshine and some of the most complex and arduous mathematics of the 20th century.
In our version of the house of mirros, behold: Nim and Fractals  what could go better together? The amazing Tany Khovanova provides us with the background on her latest paper with one of her high school students in MIT's PRIMES project
But you obviously cannot get enough! Well, then, we dare you to follow The Aperiodical's Peter Rowlett into the long, long list of podcasts for university math students. Only the bravest have listened to them all!
As immortal challenges go, Chris Burke of (x,why?) celebrates overcoming one: the 30 posts in 30 days blogging challenge with a fine post on the struggle students face with piecewise functions.
For the craziest ride of this carnival, be sure to stop by Matifutbol where, just in time for the start of the World Cup 2014 in Brazil, Herminio's post on trees and googols at the World Cup will take you on a wild trip to all possible competitions, the WedderburnEtherington number and the very edge of the known universe, making you appreciate how simple life will be over the next 4 weeks.
If this is too wild, get your dose of World Cup math blogging at Matt Scroggs's who will tell you how many Panini packages you really need to buy to complete that Panini book you've been hiding under your bed all these years.
The strongest man in the world cannot resist the powers of set theoretical forcing. And Asaf Karagila will make sure you won't wrongly use the analogy of field extensions to explain forcing.
And as you leave this Carnival behind, excited, exhausted, and content, you might still turn back for that one last ride, that one last attraction. So head over to Patrick Honner / Mr Honner as he takes on the The Grant Wiggins Conceptual Understanding Challenge, allowing us, through his response, a peek into that insightful brain of his.
And so the Carnival comes to an end and we move on. As we must. Always.
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But both these analogies would be wrong. They only take you so far, and not further. And if you wish to give a proper explanation to your listener, there will be no escape from the eventual logic and set theory of it all. I stopped, or at least I'm doing my best, using these analogies. I do, however, use the analogy of "How many roots does \(x^{42}2\) has?" as an example for everyday independence (none in \(\mathbb Q\), two in \(\mathbb R\) and many in \(\mathbb C\)). But this is to motivate a different part of the explanation: the use of models of set theory (e.g. "How can you add a real number??", well how can you add a root to a polynomial?) and the fact that we don't consider the universe per se. Of course, in a model of \(\ZFC\) we can always construct the rest of mathematics internally, but this is not the issue now. Just like we have a model of one theory, we can have a model for another. Continue reading...
]]>But I found myself brushing past even those few postings, so that yesterday I thought it was time to move on and remove them from my feed reader, de fact closing the "math" section of my feed reader, where all my research related feeds ended up. And then just as I am about to, I see this question and answer which, while neither spectacular or particular, reminded me why I once fell in love with set theory.
So, Asaf, I will call you Joey Zasa from now on.
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Plan del curso
Semana  Materiál  Evaluación 
1  Repaso de Álgebra Lineal I  L 11/8: Tarea 1 distribuido 
2 
Operadores lineales, matrices semejantes, Valores propios, polinomios característicos 
L 18/8: Tarea 1 devuelto J 21/8: Tarea 1 discutido 
3  Subespacios invariantes  L 25/8: Tarea 2 distribuido 
4 
Triangulación simultánea Diagonalización simultánea Dos demostraciones difíciles 
L 01/9: Tarea 2 devuelto J 04/9: Tarea 2 discutido 
5 
Sumas directas invariantes Descomposición prima 
L 8/9: Tarea 3 distribuido 
6 
No hay clases esta semana. Nótese que muchas personas tenían problemas con pregunta 8 de tarea 3. Para una discusión interesante sobre esta tema, vaya aquí. 
L 15/9: Feriado J 18/9: Tarea 3 devuelto y Examen parcial 1 
7 
Subespacios cíclicos Descomposición cíclica 
L 22/9: Tarea 4 distribuido 
8 
La forma racional Nuevos ejemplos de cuerpos</a> 
L 29/9: Tarea 4 devuelto J 02/10: Tareas 3 y 4 discutido 
9 
Formas y matrices Espacios producto interno 
L 06/10: Tarea 5 distribuido 
10 
Propiedades de productos internos El proceso GramSchmidt 
L 13/10: Tarea 5 devuelto J 16/10: Tarea 5 discutido 
11 
Proyecciones Complementos ortogonales 
L 20/10: Tarea 6 distribuido 
12 
Operadores unitarios Operadores ortogonales 
L 27/10: Tarea 6 devuelto J 30/10: Examen parcial 2 
13 
Operadores normales La ley de inercia de Sylvester 
L 03/11: Tarea 7 distribuido 
14  La clasificación de formas sesquilineales 
L 10/11: Tarea 7 devuelto J 13/11: Tarea 7 discutido 
15 
Formas cuadráticas Grupos de isometrías 
L 17/11: Tarea 8 distribuido 
16 
Secciones cónicas La teoría de relatividad especial 
L 24/11: Tarea 8 devuelto J 27/11: Tarea 8 discutido 
17  Exámen parcial 3 
Si tiene más preguntas, se puede
INCONCEIVABLE!
The kind overlords of the math blogosphere to whom we are all but humble servants, yes, the one true and eversoperiodical team at The Aperiodical have called upon yours truly to host a carnival. Not any carnival, but a blogging carnival of math.
So I invite to step into our tiny realm of mathblogging and help me host a grand show for all the world to see.
Bring me your posts, your rants, your poems.
Share idle idiosyncrasies, deranged derivations, cool calculations, and rash remarks.
Give it your best and your worst and your all. For the Carnival of Math is here and all creatures are welcome on its arena's floor.
]]>We're getting to some serious results here. The "tree characterization" of centrality is, I think, not known (or not appreciated) widely enough. It might be a lot to wrap your mind around as a student but this might be one of the better ways of providing some insights into the notion of cwpws sets.
This page is very amusing. The random note on destroying strongly summable ultrafilters is what occupied a large part of my postdoctoral research. Apparently it took me a while to realize this is an interesting question. Come to think of it, Francois and I also spent quite a bit of time on the tree characterization; makes me want to skip ahead to a postdoc notebook...
]]>It's a short little proof that the classic downward LöwenheimSkolem theorem is equivalent to \(\DC\), and that for a wellordered \(\kappa\), the downward LöwenheimSkolem asserting the existence of models of cardinality \(\leq\kappa\) is in fact equivalent to the conjunction of \(\DC\) and \(\AC_\kappa\). Continue reading...
]]>Clearly, the theme is different now. I also changed the content of the Papers page. I removed the abstracts (for some reason I thought this is going to be a cool thing to have, but with time it grew to annoy me greatly). I will definitely post a few things there in the coming time, some notes and eventually some nice papers  I hope! Continue reading...
]]>This page contains the proof of Theorem 3.4 of the previous part (I guess I should've included that yesterday). I can't really make much of it. It's the dull of writing up a new notion. But if you look closer, you might stumble over a few details (as I did when I took these notes). Writing this up just now I find the choice of \(w\) quite striking.
]]>We're back to Sabine Koppelberg's talks about basic \(\beta S\) results (with four more pages to come). This time, tackling the notsobasic notions of collectionwise thick/pws sets. These notions are cricital for analysing sets the minimal ideal  and equally elusive.
I'm not very happy with notation here; it seems to sacrifice accessibility over corrrectness. A sloppier notation might be helpful. In addition, "collectionwise" is a cumbersome prefix. I'd go for "uniformly" or "coherently" as they are often used in the context of filters (and this is what "collectionwise" is all about). But it probably wouldn't help to add yet another terminology.
Funny thing. I actually spent my last few weeks in Michigan thinking about these notions.
This finishes the attempts to solve 4.1.7 from Hindman&Strauss (successfully). Given the nice write up of the solution, I'm guessing I worked the proof out someplace else (blackboard, separate piece of paper etc). This reminds me that in the office I was working in at the time I found this wonderful stack of thick letter size paper (letter size! in Germany!). I loved writing on the paper for rough drafts, preparing talks/lecture notes etc. But it clashed with my desire to keep notebooks.
This page is extremely fascinating for me because of the final question. It's always easy to ask yourself if the reverse of a proposition holds; that's just standard. In this case, the answer should be a pretty straight forward "no"; however, I don't think I ever worked out a counterexample.
But that's not what makes this so fascinating for me. What is fascinating is that I spent a lot of time during my postdoc to solve a very similar problem (and failed) which I consider one of the most interesting questions about idempotent filters. Unfortunately, I was unable to solve the question. I don't want to go into detail here and it will take months until we get to that (a teaser never hurts, right?). It's fascinating to see that I was very nearly thinking about the very same problem this early in my PhD (and, not surprisingly, missed the actually interesting question at this point).
I find this double page (and the one following it) quite interesting. Mathematically speaking, there's very little going. If I recall correctly, it was Stefan Geschke (or else Sabine Koppelberg) who had mentioned the fact to me that sets in ultrafilters that are sums have too many small gaps, i.e., the size of gaps in their enumeration does not have an (improper) limit. So I found the exercise in Hindman&Strauss and tried to solve it.
What's interesting is how I went about solving it. I would call this the "formalist approach", i.e., by manipulation of symbols following simple logic since I have no intuition of the subject. Of course, I fail, repeatedly; the solution will be found on the next page.
By the way, the first two lines are about the grading of a set theory course (the previous page contains more but I did not reproduce it). I will skip a rant about how PhD students are often forced into TA duties without being paid; in a logical twist, they often "cannot" be paid because they are on grant money and most grants directly prohibit teaching duties.
]]>The previous page is followed by another attempt of research ideas.
First there's a note on a basic but important observation for \(\beta \mathbb{N}\)  it contains lots of copies of \(\mathbb{Z}\). I remember trying to figure this out and ending up asking Sabine Koppelberg  and the solution took two second, leaving me miserably disappointed by my failure.
To understand the second part of the note, I should explain that my Diplom thesis was about large cardinals and reflection principles. The first few things I tried that summer came out of that perspective  looking at cardinals (as a semingroup with ordinal addition/multiplication), hoping to connect with large cardinal theory. Nothing ever came of it but perhaps we'll encounter that later in this workbook.
]]>Finally, a first note that is not some lecture note but (almost) a note on research. Not that it's particularly meaningful or even sensible. In fact, it's rather mysterious to me. At first I thought the background lies at TOPOSYM (which I visited during the summer), where Jana Flašková talked about Ppoints. But looking back at my notes on her talk (in the red workbook but not published here), I don't think this really fits (but I might be wrong).
Practical matters
Lecture notes
Exercises
I will provide full answers for the first set, thereafter answers will only be provided on request.
Background reading
No one text covers all of the material in this course. Principal texts are as follows:
Additional texts of interest:
I have ecopies of most of the texts listed above and can provide them on request.
]]>Background on expanders:
On the sumproduct phenomenon. The basic text is Tao and Vu “Additive Combinatorics”. Here are a few other links:
On growth in nonabelian groups:
Expanders from groups:
Sieving:
Property T: The first construction of expander graphs was by Margulis and used property T, a representation theoretic property that holds for certain discrete groups (SL_d(Z) with d>2 for instance).
More wonderful stuff about thick, piecewise syndetics, and central sets.
The lemma tells us that pws could be called "almost thick"  a finite set of translations is enough to make a pws set thick. The proposition on the other hand tells us that pws is surprisingly close to being central  just one translation! (just keep in mind they are very much not the same notion). In addition, such a translation happens very, very frequently (a syndetic set!).
Somehow, I find this to be a lot of fun even if it's not particularly surprising  minimal idempotent ultrafilters are just so incredibly rich.
]]>Same lecture, new chapter. This is the first of two pages on the basics of thick sets.
"Thick" is an odd notion. It always seems a little made up to me, something stated after the fact (after asking "what does a set look like that covers a left ideal?"). On the other hand, for \(\omega\), I can imagine that the notion "a set that contains arbitrarily long intervals" might actually come up independently of ultrafilters. However, I don't know the history of the notion, so I'm probably wrong here (if you know anything about this, please leave a comment).
A technical note. I realized that using the section heading "partial translation" was a bit misleading; as would be "augmented/corrected translation". In fact, I do both  leave some things out (negligible comments etc), clear up the layout, and add corrections (e.g. \(\vert I_ n\vert = n+1\) instead of \(n\)). So I will just call it "translation" from now on.
]]>Folgerung: Ann. \(1_S\) ex., \(X = 2^S\).
\(S = (\omega, +)\)
Wir wissen
Fuer \(C \subseteq \omega\):
Also zentrale Mengen analytisch!
Frage: echt analytisch? SK: wahrscheinlich.
Notiz: Rand Oben: ?: Dieses DS in irgendeinem Sinn universell?
Notiz: gegenueberliegende Seite:
Conclusion: Assume an identity \(1_S\) exists, \(X = 2^S\).
\(S = (\omega, +)\)
We know
For \(C \subseteq \omega\):
So central Sets are analytic!
Question: properly analytic? Sabine Koppelberg: probably.
Note (across the page)
This is a curious (double) page. I don't know why Sabine Koppelberg thought it was important to add the observation that the set of central sets of \(\omega\) is analytic (and I'm wondering if the question about "properly analytic" came from my PhDsibling Gido ScharfenbergerFabian). I don't think I've ever seen this fact used in the wild. It is a nice observation though and lets me add the first entry in this transcription project with the following subsection:
Satz (AuslanderEllis) \(X\) DS ueber \(S\), \(x\in X\) => \(\exists y \in X: x \text{ prox } y\) & uniform rekurrent
Def. \(C\) dyn. zentral \(:\Leftrightarrow\) es ex. DS \(X\) ueber S, \(x,y \in X\), \(x\) prox \(y\), \(y\) unif. rek., und \(\exists U \in \mathfrak{U}(y): C = R(x,U)\).
Satz (Bergelson, Hindman etc) \(C \subseteq S\) zentral <==> \(C\) dyn. zentral.
Theorem (AuslanderEllis) \(X\) dynamical system over \(S\), \(x\in X\) => \(\exists y \in X: x \text{ proximal } y\) & uniformly recurrent
Definition. \(C\) dynanmically central \(:\Leftrightarrow\) there exists. dynamical system \(X\) over S, \(x,y \in X\), \(x\) proximal \(y\), \(y\) unif. recurrent, and \(\exists U \in \mathfrak{U}(y): C = R(x,U)\).
Theorem (Bergelson, Hindman etc) \(C \subseteq S\) central <==> \(C\) dyn. central.
This is the continuation of lecture with notes on the previous pages and contains the next notes from the next lecture.
This lecture starts where the last one left off, reaping the rewards  the famous theorem by AuslanderEllis now looks almost distressingly easy, with a terribly arbitrary choice of \(\epsilon\).
The theorem by Hindman and Bergelson (citation needed) is less known perhaps. It greatly simplifies thinking about central sets and is really quite central (pardon the pun).
]]>Not much to say here; just finishing the proof of the theorem with some simple corollaries. The notes are very short on details but it seems to be all there.
This finishes the first lecture in the workbook (the next one was apparently scheduled for Wednesday, 10am).
In a sense it's a very "normal" proof in this field. That isn't to say it's easy but while the proof is a bit of a grind (a and b being the really only interesting part), the arguments are typical arguments that appear frequently; e.g., how to use syndeticity to build an ultrafilter (in this case using a net), the powerful properties of minimal left ideals (and their somewhat horrific lack of discernable structure).
]]>The talk/lecture from the previous page continues, tackling proximality with its basic characterization in terms of \(\beta S\) and starting the proof of the characterization of uniform recurrence. That's fairly basic stuff (in the sense of necessary knowledge, not "trivial" or "easy"). The notes are a bit incomplete overall  not sure if I was too lazy (likely) or if Sabine Koppelberg jumped a bit to get to the interesting bits.
The proof that begins at the bottom of the page is, for me, a typical cases of a proof that prevents one from learning; a picture perfect proof that throws elegant arguments around but keeps from its reader the beautiful messiness of coming up with it in the first place.
The reference [HS 4.39] is alomst certainly whatever is numbered 4.39 in Hindman & Strauss, "Algebra in the Stone–Čech compactification". (I can't check the actual detail since my copy of H&S is still on route from LA.)
I forgot to mention in the first post that I substituted \mathfrak for Sutterlin in the transcription  Sutterlin is too hard to come by (Sutterlin U is used to indicate the neighborhood filter).
]]>My first workbook starts likemost would  with lecture notes.
IIRC, these notes come from series of talks Sabine Koppelberg (my PhD advisor at FU Berlin) gave over the summer 2006 to a small audience (possibly just me? I don't remember). These talks followed her lecture notes for the course "Ultrafilter, Topologie und Kombinatorik" she gave in the previous semester on all things \(\beta S\). The content is mainly based on Hindman, Strauss, Algebra in the Stone–Čech Compactification, greatly improved by Sabine's own style.
The next two pages will continue this talk and ~20 pages will follow on the subject (interrupted by exercises and other notes). The topic are dynamical systems and recurrence, the famous BergelmanHindman result (as indicated: central = dynamically central), some notes on thick, pieceswise syndetic and the combinatorial description of central as well as the Central Sets Theorem.
It's funny to see how very inexperienced I was, e.g., the note on the product topology  I really didn't know that? Wow. Then again, I never took a topology course while getting my Diplom (I could have used a better advisory infrastructure).
It's also funny (and somewhat alarming) to see how many subjects came up this early. But we'll get to that...
]]>Arbeitsheft, 13. August 2006 bis 28. März 2007
Workbook, 13. August 2006 to 28. März 2007
This is the opening page of my first workbook, just after I had started to work on my PhD seriously (having finished my Diplom in Munich a few months earlier).
I'm using p1
in the title to be intentionally vague  while this happens to be page 1, I don't intend to publish every page, so the p
might be read as page
, part
, or piece
.
This workbook starts with a journal entry regarding traveling to TOPOSYM 2006 and continues with notes on the talks at TOPOSYM. It is curious to read those personal notes. For example, my first meeting with Wistar Comfort with whom I happened to share a close personal friend is notable mostly for the embarrassment I felt while being introduced to lots of researchers (whom WW Comfort all knew) whose name I barely caught (and never remembered) and with whom I wasn't able to have a conversation.
I won't reproduce the notes on conference talks  they are neither interesting nor complete (and they deteriorate over the course of the week). I don't remember any of the talks now, but I remember the "performance" of some of the speakers (mostly the distinguished ones, like WW Comfort sharing stories from TOPOSYM during the Cold War). I do fondly remember spending that week with my fellow PhD students, Gido Scharfenberger and Steffi Frick, and getting the first taste of being among researchers  exhilarating.
Comments
A big part of this would be an effort to digitalize my handwritten notebooks. But what is a good platform? I could blog them, page after page, transcribing them and annotating the images. But perhaps a MediaWiki is a more suitable alternative? After all, searching navigating blog posts isn't exactly easy. Or perhaps both (should just be copy&paste).
Perhaps I should use image annotations to directly markup the images? Perhaps I should wait for Hypothes.is to support this? Also, pushing things to figshare would allow people to reference every note with DOI etc  that's great, no? But are there other tools? Better tools? I have no clue. Help would be appreciated.
Well, as you might have guessed, this draft has been sitting here for the last 6 months. So instead of waiting for the perfect solution, I'll start with the straight forward and reliable one. One blog post per page, transcribing the page, possibly adding translations, notes, comments. Since my notebooks sometimes contain personal notes, I will not necessarily publish every page of every notebook. For the same reason, I might blur parts of a page etc. Hopefully, this won't be too much of a mess (and interesting to someone, at least give them a laugh or something). We'll see how it goes.
Comments
For the next few months I'll be in Bonn. As you can see, it's not for the weather.
Is there anything making this move worth while?
Yes, definitely.
]]>It's been a fun 1½ years in LA. Time to move.
Comments
I find that frustrating. So let's not do this. This is a test post to check out Jetpack connect and find a way to multishare to different social networks.
Alright, not too bad. Here's what this was about. Jetpack offers autoposting to a bunch of social networks, including my two current active ones  twitter and Google+. In particular the Google+ connection is painfully difficult with free tools. But still, a large amount of people I want to share things with are there. However, I strongly believe in my website being my primary digital outlet. I don't want to post content that will just be on Twitter or just on Google+. It is mine and should be shared from my website.
In addition, I have been thinking about how to write more frequently. One good piece of advise is to write less but more often. But I also find myself wanting to post different, more social content, e.g. a simple photo, share a link. One obvious tool is my phone and tablet. It has apps for all my networks as well my reading applications. A simple idea would be a multishare app that would allow me to push shared content to all the apps I care about. Luckily, I couldn't find a well working one long enough to remember Jetpack Connect. Luckily it works with the WordPress app, so I can author once wherever I am and share where I want to share.
Unfortunately, for all my three readers, this means I might start posting little pieces of crappy content. Bear with me and yell at me from time to time. Here's to moar bloggings in 2014.
]]>You might think Los Angeles and snow are separate, but surprisingly it's often not by far. Apart from the almost daily updates on NPR regarding snow packing strength during the winter (which is all about the water available the next summer), you have to drive barely two hours to find yourself in need for winter gear, being snowed in in front of a fireplace. At least I did.
Unfortunately, not as good as I'd hoped. While Google+ will at least pull in the image into the minipreview twitter won't do anything with it. That's too bad, but perhaps better than nothing.
]]>Then in the summer, the ever fantastic Tzviya Siegmann pulled me into the AAP's EPUB implementation project and so I had a chance to be active in both the features and the accessibility groups. It was an extremely interesting experience all around so just two points. First, I am amazed at the work of the group leaders, handling the difficulties of running such a complex project, in a very short time, with a highly diverse group of participants. Second, it was an experience to, well, experience antitrust concerns like that. While frustrating at times, I didn't find this tragic in the end; there was more to lose than to gain. But it felt strange to be on the other end of the stick, so to speak, wanting to drive publishers and reading systems to close collaboration so that we can finally get decent support for math & science in ebooks. The AAP white paper came out this week.
During that time I also wrote the first drafts for "MathML Forges On" (the title was a suggestion of Simon St. Laurent who has been a great editor). I want to thank Fred Wang, David Carlisle, Neil Soiffer and Dave Barton for many helpful comments and Sanders Kleinfeld for being a matchmaker, twice.
During the AAP project, I also summarized the technical details a little with suggestions for the short term. This wasn't useful to the AAP project but there's no reason to throw it away  so here it is.
Note. This was written with the following question in mind: how can we speed up MathML adoption in epub3? Well, one way would be to understand what level of support can be achieved in the short term. Since full MathML 3 support is simply not available, compromises have to be made. This means creating guidelines for publishers to ensure their content can be supported and for reading systems to understand how they can support that level. And for both sides to push each other  publishers, pushing reading systems by