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Compact object and compact generator in a category
improved the second paragraph
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Is there the longest geodesic?
Mozibur says his comment above was intended as a joke.
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Proof of continued fraction identity of subfactorial
snark removed
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Infinite tridiagonal matrices and a special class of totally positive sequences
I'm sure you're striving to optimize this post, but please be aware that each edit bumps this post to the top of the stack and other posts (also vying for attention) down. So if you could condense several improvements into an edit, rather than changing by a single character, it would be appreciated.
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What makes dependent type theory more suitable than set theory for proof assistants?
@TimothyChow Thanks; I listened again and you're right. Still, I'm not sure how to take this assertion of "doing nothing".
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What makes dependent type theory more suitable than set theory for proof assistants?
I hope Buzzard joins the discussion. But one thing I found strange is this mention of "chaps" around Voevodsky who haven't done anything with Coq except formalize rings and modules. Did I hear that correctly? It sounded really misleading. Clearly there are extensive libraries of math formalized by Coq; for example, the formalization of the odd order theorem (finite groups of odd order are solvable) by Gonthier et al. was one such tour de force, although not necessarily one developed by the "Voevodsky chaps".
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Does a natural transformation of functors induce a natural transformation between their right adjoints?
What Paul says is correct, and it resonates most convincingly when you hear an Australian category theorist say it. (I tend to be somewhat lax [haha] in my usage, where any morphism you derive from an adjunction in similar fashion could also be called a "mate". For example, in informal chat, I might also refer to Maxime's $id \to F^\wedge G$ as a mate.)
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Does a natural transformation of functors induce a natural transformation between their right adjoints?
Yes. Let $\eta: 1 \to F^\wedge F$ denote the unit and $\varepsilon: G G^\wedge \to 1$ the counit. Then form the evident composite $$G^\wedge \stackrel{\eta G^\wedge}{\to} F^\wedge F G^\wedge \stackrel{F^\wedge TG^\wedge}{\to} F^\wedge G G^\wedge \stackrel{F^\wedge \varepsilon}{\to} F^\wedge$$
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Would it be simpler, pedagogically speaking, if textbook writers introduced root systems as an example of a quandle?
edited out stuff not germane to the question
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Reference request: Examples of research on a set with interesting properties which turned out to be the empty set
Any idea how old he was? I don't know the history of the result that any 1-knot in 4-space is equivalent to an unknot, but for some reason thought this would have been known for a long time, even predating Zeeman's birth year.
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How to show this series converges $\sum\limits_{n=1}^\infty n^{-1/2}\sin(n)\sin(n^2)$
Convergence would follow if sums of the form $\sum_{n=1}^M \sin(n)\sin(n^2)$ had an upper bound independent of $M$. This is certainly known for sums $\sum_{n=1}^M \sin(n)$. I'm sure it's also true for these sums, but I don't have an immediate proof.
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How to put a monetary incentive on an open research problem?
I suggest you try asking your question at MO main, and see what happens. You might get an answer for free!
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Quotients of posets
@creillyucla That's right.
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Category theory and arithmetical identities
"Arithmetical identities" like $(ab)^c = a^c b^c$, $a^{b+c} = a^b a^c$, and $(a^b)^c = a^{bc}$ can all be understood in the light of cartesian closed categories. The binomial identity $(a+b)^n = \sum_j \binom{n}{j} a^j b^{n-j}$ can understood in terms of extensive categories.
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Non-homeomorphic connected $T_2$-spaces with isomorphic topology poset
Very interesting answer: +1.
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