User Reid Barton

20 votes

Least number of charts to describe a given manifold

answered Oct 26, 2009 at 16:54

20 votes

Relating category theory to programming language theory

answered Nov 5, 2009 at 15:38

19 votes

Limits in category theory and analysis

answered Dec 28, 2009 at 16:25

19 votes

Colimits in the category of smooth manifolds

answered Mar 23, 2010 at 16:46

18 votes

Accepted

Are non-empty finite sets a Grothendieck test category?

answered Jan 7, 2010 at 17:57

18 votes

Why forgetful functors usually have LEFT adjoint?

answered Nov 23, 2009 at 4:50

18 votes

Is it possible to capture a sphere in a knot?

answered Dec 8, 2009 at 17:13

18 votes

Is there an infinity × infinity lemma for abelian categories?

answered Nov 7, 2009 at 21:53

17 votes

Accepted

Countable subgroups of compact groups

answered Oct 30, 2009 at 7:46

17 votes

Accepted

K-theory as a generalized cohomology theory

answered Mar 17, 2010 at 18:59

16 votes

Accepted

Mayer-Vietoris homotopy groups sequence of a pull-back of a fibration

answered Oct 30, 2009 at 6:44

16 votes

Accepted

How to think about model categories?

answered Oct 24, 2009 at 17:04

16 votes

Number of permutations with a specified number of fixed points

answered Dec 21, 2009 at 17:09

15 votes

Accepted

How cavalier can I be when demanding a category have direct sums?

answered Feb 15, 2010 at 21:07

15 votes

Accepted

Is the singular simplicial complex functor $\operatorname{Sing}_\bullet:\operatorname{Top} \to \operatorname{sSets}$ fully faithful for nice spaces?

answered Mar 20, 2023 at 7:07

14 votes

Are there any important mathematical concepts without discrete analog?

answered Mar 10, 2010 at 23:48

14 votes

Accepted

Do h-coequalizers and coproducts give all h-colimits?

answered Jan 27, 2010 at 20:18

14 votes

Accepted

yoneda-embedding vs. dual vector space

answered Dec 28, 2009 at 2:00

13 votes

Is the semigroup M(n, Z) finitely presented? If so, where can I find a presentation of it?

answered Feb 10, 2010 at 1:40

13 votes

What are the auto-equivalences of the category of groups?

answered Jan 6, 2010 at 23:00

13 votes

Why do finite homotopy groups imply finite homology groups?

answered Dec 20, 2009 at 15:35

13 votes

Upper bound on the area of a midpoint pentagon?

answered Nov 15, 2009 at 21:00

13 votes

One Point Compactification

answered Oct 27, 2009 at 17:41

13 votes

Accepted

Two finite groups with the same identical relations?

answered Oct 15, 2009 at 18:43

13 votes

What is the minimum N for which there exist N points in the plane that cannot be covered by any number of non-overlapping closed unit discs?

answered Apr 6, 2010 at 23:52

13 votes

"Models" in homotopy theory

answered Nov 13, 2021 at 15:51

12 votes

Accepted

Taking the category of sheaves is symmetric monoidal

answered Aug 13, 2021 at 13:58

12 votes

Accepted

Why the search for ever larger primes?

answered Oct 17, 2009 at 18:53

12 votes

What are examples of good toy models in mathematics?

answered Oct 20, 2009 at 5:50

12 votes

Accepted

Which commutative rigs arise from a distributive category?

answered Oct 24, 2009 at 15:19

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202 Answers

Least number of charts to describe a given manifold

Relating category theory to programming language theory

Limits in category theory and analysis

Colimits in the category of smooth manifolds

Are non-empty finite sets a Grothendieck test category?

Why forgetful functors usually have LEFT adjoint?

Is it possible to capture a sphere in a knot?

Is there an infinity × infinity lemma for abelian categories?

Countable subgroups of compact groups

K-theory as a generalized cohomology theory

Mayer-Vietoris homotopy groups sequence of a pull-back of a fibration

How to think about model categories?

Number of permutations with a specified number of fixed points

How cavalier can I be when demanding a category have direct sums?

Is the singular simplicial complex functor $\operatorname{Sing}_\bullet:\operatorname{Top} \to \operatorname{sSets}$ fully faithful for nice spaces?

Are there any important mathematical concepts without discrete analog?

Do h-coequalizers and coproducts give all h-colimits?

yoneda-embedding vs. dual vector space

Is the semigroup M(n, Z) finitely presented? If so, where can I find a presentation of it?

What are the auto-equivalences of the category of groups?

Why do finite homotopy groups imply finite homology groups?

Upper bound on the area of a midpoint pentagon?

One Point Compactification

Two finite groups with the same identical relations?

What is the minimum N for which there exist N points in the plane that cannot be covered by any number of non-overlapping closed unit discs?

"Models" in homotopy theory

Taking the category of sheaves is symmetric monoidal

Why the search for ever larger primes?

What are examples of good toy models in mathematics?

Which commutative rigs arise from a distributive category?