@oantolin@mathstodon.xyz avatar

oantolin

@oantolin@mathstodon.xyz

I'm a mathematician at UNAM in Mexico City. I work in algebraic topology, homotopy theory and higher category theory, but am interested in all sorts of math.

I also enjoy computer programming as a hobby and am a big fan of the text editor Emacs.

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dekkzz76, to emacs
@dekkzz76@emacs.ch avatar

Are many people running the emacs 30 apk on android?

oantolin,
@oantolin@mathstodon.xyz avatar

@evgandr @dekkzz76 How did you manage to use Emacs 30 a long time ago? Did you mean a different version of Emacs instead?

oantolin, to random
@oantolin@mathstodon.xyz avatar

Great visual introduction to the concept of Pareto front in optimization.

https://alis.me/x/the-hottest-wheels/

christianp, to random
@christianp@mathstodon.xyz avatar

The good thing about my name is that when the github issue tracker truncates it, it gives the right energy

oantolin,
@oantolin@mathstodon.xyz avatar

@christianp That's fantastic! 🙂

JonathanAldrich, to random
@JonathanAldrich@social.sigsoft.org avatar

Don't manipulate your citation count by putting irrelevant citations to your work in your own papers, or requiring other people to do it when you review their papers. This is an example from the IEEE, but the ACM pubs board actively polices this too.

https://retractionwatch.com/2024/05/14/professor-former-dean-earns-nearly-100-expressions-of-concern-for-citation-manipulation/

oantolin,
@oantolin@mathstodon.xyz avatar

@JonathanAldrich @jonmsterling

MartinEscardo, to random
@MartinEscardo@mathstodon.xyz avatar

It is just me? The following definition of category hurts my categorical instincts, because it uses object equality.

A category consists of

  1. A collection of objects.

  2. A collection of morphisms.

  3. Each morphism f has two assigned objects, its source s(f) and its target t(f).

  4. For each pair of morphisms f,g such that t(f)=s(g) there exists a specified morphism g ∘ f such that [it doesn't matter what]

  5. [Some axioms are satisfied.]

It is (4) that hurts my categorical instincts.

There is no reason to have "evilness" (in the categorical sense, rather than the emotional sense) built-in in the definition of category!

This definition is, for example, adopted by Freyd.

oantolin,
@oantolin@mathstodon.xyz avatar

@MartinEscardo "There is no reason to have "evilness" (in the categorical sense, rather than the emotional sense) built-in in the definition of category!"

If you mean that mathematicians could instead adopt a definition of category in dependent type theory where the morphisms are a dependent family a, b : C₀ |- C(a,b), then I would say there is a reason we usually don't do that: ignorance of type theory. Most mathematician know little about foundations, and what little we know is usually phrased in first order logic with equality, not type theory.

BartoszMilewski, to random
@BartoszMilewski@mathstodon.xyz avatar

I'm struggling with the definition of the category of elements--the direction of morphisms. Grothendieck worked with presheaves (C^{op} \to \mathbf{Set}), with a morphism ((a, x) \to (b, y)) being an an arrow (a \to b) in (C). The question is, what is it for co-presheaves? Is it (b \to a)? nLab defines it as (a \to b) and doesn't talk about presheaves. Emily Riehl defines both as (a \to b), which makes one wonder what it is for (𝐶ᵒᵖ)ᵒᵖ→𝐒𝐞𝐭 , not to mention (C^{op}\times C \to \mathbf{Set}).

oantolin,
@oantolin@mathstodon.xyz avatar

@BartoszMilewski There are two possible conventions and both work (this happens a lot in math, specially in category theory with all the op's —and things get worse in 2-category theory which has op's and co's which you can pick independently!). You can use a→b which produces a category with a functor E→C which is a discrete opfibration, or you can use b→a to get a category with a functor E→C^op, which is a discrete fibration. Neither is better or worse than the other. I usually choose depending on whether fibration or opfibration is more natural for what I want to later.

oantolin,
@oantolin@mathstodon.xyz avatar

@BartoszMilewski @johncarlosbaez It does work for all those other cases too, but there is also a second possible definition which also works for all those cases. 🤷🏽

pkal, to random
@pkal@emacs.ch avatar

It seems that the transient-show-popup option is exactly what you are looking for.

oantolin,
@oantolin@mathstodon.xyz avatar

@pkal Is this a standalone post? It feels more like a reply.

loke, to random
@loke@functional.cafe avatar

This answer came from a post on Quora, and where the posted got the answer from should be obvious.

Oh, and the date is wrong. The actual date that particular statement was posted was this year.

oantolin,
@oantolin@mathstodon.xyz avatar

@loke Somebody forgot to tell J it's impossible to count the primes under 10⁹.

By the way, is there a version of Kap for Android?

johncarlosbaez, (edited ) to random
@johncarlosbaez@mathstodon.xyz avatar

It's time to have that talk with your kid. About quantum mechanics:

https://www.smbc-comics.com/comic/the-talk-3

oantolin, (edited )
@oantolin@mathstodon.xyz avatar

@johncarlosbaez I hope I'm missing something but a quick glance at the paper suggests Barandes doesn't actually get around the problem at all. He says quantum systems are given by time-dependent stochastic matrices Gamma(t) which are "unistochastic" meaning they are given by s(U(t)) where U(t) is unitary. The Hamiltonian is determined by U(t) in the usual way. I might be missing something but I wouldn't call this a formulation that avoids complex numbers and unitary matrices...

cory, to random
@cory@social.lol avatar

Present me with the Shakespeare’s Hamlet, but written in the tone of an author that ardently believes only eMacs should be used to write such a work.

oantolin,
@oantolin@mathstodon.xyz avatar

@cory @hl I'm surprised that's what you wanted. Since you wrote "eMacs" I thought you meant these computers: https://en.wikipedia.org/wiki/EMac

ColinTheMathmo, to random
@ColinTheMathmo@mathstodon.xyz avatar

Asking for a friend(*) ...

"I need to brush up on some Pure Maths for a thing, and I find I'm pretty rusty. Can any of m'Maths friends recommend a good book on rings and ideals, and that end of algebra?"

(*) No, really ...

oantolin,
@oantolin@mathstodon.xyz avatar

@ColinTheMathmo I like Kaplansky's Fields and Rings.

brokenix, to random
@brokenix@emacs.ch avatar

> you mostly model data with sum types, which in my mind are the best way to model data

True its quite strict in Haskell though
https://blog.darklang.com/leaving-ocaml/

oantolin,
@oantolin@mathstodon.xyz avatar

@brokenix Don't people model data with sum types and product types used in roughly equal measures? Is it really mostly sums? That sounds off to me.

oantolin,
@oantolin@mathstodon.xyz avatar

@boarders @brokenix It does seem possible that's what was meant.

christianp, to random
@christianp@mathstodon.xyz avatar

With delimiters so mathstodon will render it:

[ \frac{\left(n!\right)^2}{2}\sum _{k=0}^m\frac{1}{n-k}{n-k \choose k}^2 ]

oantolin,
@oantolin@mathstodon.xyz avatar

@christianp Do you know of any Android Mastodon clients that render LaTeX?

oantolin,
@oantolin@mathstodon.xyz avatar

@christianp Thanks for the recommendations. I also discovered that the Trunks app renders LaTeX but unfortunately uses $$...$$ delimiters (and for inline math!). I filed a feature request for () and []. https://github.com/trunks-social/trunks-public/issues/301

ibrahimtencer, to random
@ibrahimtencer@mathstodon.xyz avatar

The Borsuk-Ulam theorem implies that at any time there are antipodal points on earth with the same temperature and pressure. Is it possible to actually track where those points are? Would be cool if a website could display that and track it in real time.

https://en.wikipedia.org/wiki/Borsuk%E2%80%93Ulam_theorem

oantolin,
@oantolin@mathstodon.xyz avatar

@boarders Yeah, clearly this one should have been called the temperature continuity hypothesis.
@MartinEscardo @antopatriarca @ibrahimtencer

MartinEscardo, to random
@MartinEscardo@mathstodon.xyz avatar

Today I met a student at MGS who introduced themselves as "from mastodon". 🙂

Hi.

oantolin,
@oantolin@mathstodon.xyz avatar

@christianp Yes! I started out following only people I knew in person but by now it's mostly potential figments.
@MartinEscardo

koantig, to windows
@koantig@mamot.fr avatar

What's a good software for drawing and writing maths on a tablet?

I had to do it in a pinch today to explain something to a colleague, and ended up using PowerPoint as a canvas. Let's just say it was not ideal.

I'm thinking: easily delete the last doodle, draw straight lines, switch colours, infinite canvas, that kind of things.

It's for work, so I'm looking for a solution unfortunately.

oantolin,
@oantolin@mathstodon.xyz avatar

@koantig Microsoft OneNote seems pretty good.

MartinEscardo, to random
@MartinEscardo@mathstodon.xyz avatar

Dialogue between a constructive mathematician and classical mathematicians.

Constructive mathematician. A or not A, right?

Classical mathematicians. Nod.

Constructive mathematician. For any two mathematical statements A and B, either A implies B or B implies A.

Classical mathematicians. What?

This was in a talk by the late Roy Dyckhoff in 1999 in St Andrews for an audience of mathematicians. If I remember correctly, the title of his talk was "the logic of linear implication" (nothing to do with linear logic, but instead with Dummett).

oantolin,
@oantolin@mathstodon.xyz avatar

@MartinEscardo Classically, (a => b) v (b => a) is equivalent to for ~a v b v a v ~b which is true by excluded middle (for either a or b, two reasons!)

(By the way, in your example the implication I believe is that the continuum hypothesis implies the axiom of choice 😛)

A similar thing that I find comes up fairly often is that someone will say that two theorems are equivalent and someone else will say, "Of course they are, they're both true, aren't they?".

My standard response in that situation is to say that when I say two theorems are equivalent it is not a mathematical claim, it's a statement about human psychology: what I mean is that it is easier for people to prove one theorem assuming the other than to prove either theorem from scratch.

oantolin,
@oantolin@mathstodon.xyz avatar

@boarders @MartinEscardo But I do have reason to think I won't make those claims of complexity precise, so let me continue to make my psychological claims. 😛

rml, to emacs
@rml@functional.cafe avatar

I've been using ivy-mode forever and don't know what I'm missing wrt to its many successors. What should I try?

oantolin,
@oantolin@mathstodon.xyz avatar

@rml I love Vertico as a completion UI, because in a addition to showing completions in a vertical list (like Ivy) in the minibuffer, it can also show them in a grid, a horizontal line, show only the top completion or show completions in a dedicated buffer for extra real-estate. You can switch views on the fly and configure the default view per command or per completion category.

Vertico is only a completion UI, it does not determine which completion candidates match against what you type. For that I sheepishly recommend my own Orderless package, which is a highly configurable completion style for Emacs.

To replace Counsel, I recommend Consult, which is not tied to any particular completion UI but works great with Vertico (and also with the default completion UI or with the built-in icomplete UI).

To replace Ivy's actions I'll (also sheepishly) recommend my own Embark package, which lets you run any Emacs command whatsoever as an action, not only on minibuffer completion candidates but also on stuff you find in regular buffers.

oantolin,
@oantolin@mathstodon.xyz avatar

@grtcdr @rml What completion styles do you use? (And if you don't use Orderless, I'll sheepishly recommend it to you too 😛)

johncarlosbaez, (edited ) to random
@johncarlosbaez@mathstodon.xyz avatar

If you want Putin to completely crush Ukraine, don't vote for Biden. Let Trump win.

Trump installed his daughter-in-law and a guy named Whatley to run the Republican party. Now Whatley has listed Ukraine as an "aggressive adversary" of the US, along with China and Iran.

I'm only amazed at how open he's being about this. The alliance between Putin and Trump against Ukraine has been clear for a long time.

In case you forget, in 2019 the House of Representatives released a report saying

"The impeachment inquiry has found that President Trump, personally and acting through agents within and outside of the U.S. government, solicited the interference of a foreign government, Ukraine, to benefit his reelection. In furtherance of this scheme, President Trump conditioned official acts on a public announcement by the new Ukrainian president, Volodymyr Zelenskyy, of politically-motivated investigations, including one into Joe Biden, one of Trump's domestic political opponents. In pressuring President Zelenskyy to carry out his demand, President Trump withheld a White House meeting desperately sought by the Ukrainian President, and critical U.S. military assistance to fight Russian aggression in eastern Ukraine."

Zelenskyy didn't knuckle under and the rest is history.

(1/2)

https://www.newsweek.com/trump-rnc-chair-whatley-says-ukraine-us-adversary-republicans-1887731

oantolin,
@oantolin@mathstodon.xyz avatar

@johncarlosbaez @MartinEscardo This discussion reminded me of Ralph Nader's novel "Only the Super-rich can save us!" (which I haven't read but am mildly curious about).

https://en.m.wikipedia.org/wiki/Only_the_Super-Rich_Can_Save_Us!

galdor, to random
@galdor@emacs.ch avatar

Some say you must start with a simple programming language and learn your way up. Others tell you to learn a low level language such as C to understand how everything works.

I've seen plenty of developers who started with Python or JS, and some who started with C. Comparing them, there is no doubt about which method yields the best developers.

The good news is that it's never too late to go back to the fundamentals.

oantolin,
@oantolin@mathstodon.xyz avatar

@galdor Another approach illustrated by great books like Djikstra's "A Method of Programming" or Gries's "The Science of Programming" or Morgan's "Programming from Specifications" is to learn programming in the abstract using some semi-informal pseudocode notation. After all, what do you need a real programming language for before you know how to program? (I'm only about 80% kidding —I recognize the value of experimenting on the computer while learning to program— but that 20% is maybe what you'd expect from a mathematician).

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