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Questions that are about research in mathematics, or about the job of a research mathematician, without being mathematical problems or statements in the strictest sense. Do not use this tag for easy or supposedly easy mathematical questions.

29 votes

Is a come back to mathematical research possible?

I hesitate to posit myself as an example, but I was out of academia from 2001 to 2019, when I decided to become a stay-at-home dad while my wife became the breadwinner. (I won't go into the details of …
3 votes

What's a great christmas present for someone with a PhD in Mathematics?

A book of interviews of famous mathematicians could be good. I have in mind particularly More Mathematical People, which I've gotten a lot of mileage from here at MathOverflow.
6 votes

Would it be simpler, pedagogically speaking, if textbook writers introduced root systems as ...

You might find useful certain aspects of Alissa Crans's thesis, Alissa Crans, Lie 2-Algebras, Dissertation, U. Cal. Riverside, 2004 (link). For instances, Lie groups and their associated Lie algebra …
Todd Trimble's user avatar
  • 53.3k
16 votes

A map of non-pathological topology?

I'll go ahead and say that Polish spaces are an interesting and almost sui generis class. There is a rich literature of applications to and from descriptive set theory, with layers of "pathology" hier …
Todd Trimble's user avatar
  • 53.3k
9 votes

Examples of notably long or difficult proofs that only improve upon existing results by a sm...

The following example is described in The Man Who Loved Only Numbers by Paul Hoffman. There is a reasonably short proof, found by Esther Klein (later Szekeres) in 1932, that given 5 points in the pl …
4 votes
Accepted

Technical term for representing object of a presheaf determined by a left-adjoint?

As requested, I'll turn my comments into an answer. There were two questions, the first being what we call the representing object if a presheaf $c \mapsto \mathcal{D}(F c, d)$ is representable, and t …
Todd Trimble's user avatar
  • 53.3k
14 votes

Problems where we can't make a canonical choice, solved by looking at all choices at once

General topology as found in textbooks seems to be chock-full of examples where the axiom of choice seems to be (unconsciously?) invoked, and unnecessarily if one follows Eilenberg's advice to avoid s …
12 votes

What is your favorite proof of Tychonoff's Theorem?

I won't swear it's my absolute favorite, but today I learned of a nice proof due to Clementino and Tholen who take as their starting point the closed-projection characterization of compactness, viz. t …
4 votes

Locales and Topology.

As for question 2.: it's hardly recent, but since I didn't see it mentioned in this thread, let me mention that the Tychonoff theorem for locales does not require the axiom of choice and is a piece of …
19 votes

Why is Set, and not Rel, so ubiquitous in mathematics?

Taking up remarks near the end of the OP, and somewhat in line with Mike Shulman's answer, I'd like to underline the structural interplay between $\mathbf{Set}$ and $\mathbf{Rel}$ to indicate one poin …
19 votes

Applications of the Cayley-Hamilton theorem

Cayley-Hamilton can be useful in commutative algebra. Related to its close connection with Nakayama's lemma as mentioned in a comment by Qiaochu (see also Wikipedia), see for example the development g …
6 votes

Categories of finite objects

I would say you could make good headway on this by looking over some of the research projects of Tom Leinster, Mark Meckes, and Simon Willerton (and others I may be forgetting), centering on various n …
12 votes

Parodies of abstruse mathematical writing

Of course, there's this old classic: http://bjornsmaths.blogspot.com/2005/11/how-to-catch-lion-in-sahara-desert.html
17 votes

Examples of Kan extensions, adjunctions, and (co)monads in analysis, Lie theory, and differe...

One way to understand $l^1(X)$ for a set $X$ with counting measure is that $l^1(-): Set \to Ban$ provides a left adjoint to the functor $\hom(k, -): Ban \to Set$. Here $k$ is the ground field and $Ban …
0 votes

Obscure Names in Mathematics

The Hauptsatz (due to Gentzen).

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