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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.

4 votes

Trichotomies in mathematics

Here is a cluster of examples with a common theme, based partly on comments here and in an MO thread on whether an empty space should be considered connected, and partly on an article in the nLab, "to …
Martin Sleziak's user avatar
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 …
Todd Trimble's user avatar
  • 53.3k
5 votes

Which popular games are the most mathematical?

There's also Nine Men's Morris, which is a very ancient game. My understanding is that it has been effectively solved in recent years with the help of computer analysis.
Martin Sleziak's user avatar
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 …
Todd Trimble's user avatar
  • 53.3k
25 votes

Is the empty graph a tree?

The whole discussion seems to devolve on whether the empty graph (or empty space) should be considered "connected". Angelo and I are of the school that it should not, but this should be explained sinc …
Martin Sleziak's user avatar
14 votes

What are some examples of colorful language in serious mathematics papers?

From Jim Stasheff's Homotopy Associativity of H-spaces I, the magisterial-sounding To study spaces which admit $A_n$-structures, we can work directly with the maps…. In the case of a topological gro …
Martin Sleziak's user avatar
3 votes

Major mathematical advances past age fifty

Charles Sanders Peirce (born 1839) explicitly declared his Existential Graphs (all three parts: Alpha, Beta, and Gamma) to be his chef d'oeuvre. This work on graphical logic began sometime in the earl …
Martin Sleziak's user avatar
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 …
Martin Sleziak's user avatar
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.
Todd Trimble's user avatar
  • 53.3k
8 votes
Accepted

Concise definition of subobjects

Of course it's not necessary to make this identification, but it's fairly harmless since the groupoid of monomorphisms into an object $X$ is equivalent to the discrete category of subobjects, and it c …
Todd Trimble's user avatar
  • 53.3k
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
24 votes

Most memorable titles

You'd think that with John H. Conway around, this should be like shooting fish in a barrel. One title that comes to mind is The Sensual (Quadratic) Form and there are more goodies if you look at his …
Martin Sleziak's user avatar
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 …
Todd Trimble's user avatar
  • 53.3k
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

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