User Tim Campion

160 votes

37 answers

15k views

Conceptual reason why the sign of a permutation is well-defined?

asked Mar 8, 2022 at 16:55

101 votes

31 answers

28k views

Errata for Atiyah–Macdonald

asked Oct 15, 2010 at 0:56

66 votes

5 answers

6k views

Heuristic argument that finite simple groups _ought_ to be "classifiable"?

asked Sep 9, 2010 at 10:05

42 votes

2 answers

2k views

Do vector spaces without choice satisfy Cantor-Schroeder-Bernstein?

asked Oct 23, 2020 at 17:03

41 votes

5 answers

5k views

What is the cotangent complex good for?

asked Sep 20, 2020 at 4:33

41 votes

0 answers

1k views

Is there anything to the obvious analogy between Joyal's combinatorial species and Goodwillie calculus?

asked Apr 4, 2017 at 1:22

40 votes

3 answers

3k views

A map of non-pathological topology?

asked Jun 6, 2019 at 4:57

37 votes

3 answers

3k views

What is the point of pointwise Kan extensions?

asked Oct 7, 2015 at 3:10

37 votes

3 answers

2k views

Does the category of (algebraically closed) fields of characteristic $p$ change when $p$ changes?

asked Apr 8, 2016 at 0:22

36 votes

1 answer

3k views

Is there a general theory of "compactification"?

asked Oct 14, 2019 at 14:48

35 votes

2 answers

3k views

What is the relationship between connective and nonconnective derived algebraic geometry?

asked Apr 29, 2017 at 23:48

35 votes

0 answers

1k views

Is there a rigid analytic geometry proof of the functional equation for the Riemann zeta function?

asked Nov 5, 2018 at 21:20

32 votes

1 answer

2k views

What was the error in the proof of Roos' theorem?

asked Jan 20, 2018 at 22:27

32 votes

2 answers

2k views

Converse to Stokes' Theorem

asked Nov 1, 2013 at 22:03

30 votes

2 answers

2k views

Why is the motivic category defined over the site of smooth schemes only?

asked Jan 4, 2018 at 18:40

29 votes

4 answers

1k views

Varieties where every algebra is free

asked Feb 18, 2014 at 21:15

27 votes

3 answers

2k views

Where's the best place for an algebraic geometer to learn some algebraic number theory?

asked Dec 13, 2018 at 19:49

27 votes

3 answers

1k views

What is the geometric significance of fibered category theory in topos theory?

asked Sep 30, 2018 at 19:41

27 votes

0 answers

1k views

Spectral sequences as deformation theory

asked Mar 5, 2021 at 1:24

27 votes

1 answer

1k views

Is every category a localization of a poset?

asked Sep 3, 2021 at 14:02

26 votes

3 answers

2k views

Does Con(ZF + Reinhardt) really imply Con(ZFC + I0)?

asked Apr 22, 2016 at 12:21

25 votes

2 answers

1k views

Are "most" spaces aspherical?

asked Apr 12, 2019 at 17:17

25 votes

1 answer

1k views

What are Koszul dualities?

asked Feb 24, 2021 at 20:45

23 votes

5 answers

3k views

What are _all_ of the exactness properties enjoyed by stable $\infty$-categories?

asked Apr 15, 2017 at 1:01

23 votes

3 answers

1k views

Why the stable module category?

asked Apr 30, 2023 at 22:36

23 votes

3 answers

2k views

What are some toy models for the stable homotopy groups of spheres?

asked Dec 1, 2023 at 20:59

22 votes

1 answer

1k views

What's with equivariant homotopy theory over a compact Lie group?

asked Sep 1, 2017 at 2:12

21 votes

3 answers

2k views

Why is Kan's $Ex^\infty$ functor useful?

asked Mar 6, 2019 at 1:03

21 votes

1 answer

2k views

Is algebraic $K$-theory a motivic spectrum?

asked Jun 19, 2018 at 18:06

21 votes

3 answers

1k views

Which $\ast$-algebras are $C^\ast$-algebras?

asked Sep 27, 2019 at 14:14

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446 Questions

Conceptual reason why the sign of a permutation is well-defined?

Errata for Atiyah–Macdonald

Heuristic argument that finite simple groups _ought_ to be "classifiable"?

Do vector spaces without choice satisfy Cantor-Schroeder-Bernstein?

What is the cotangent complex good for?

Is there anything to the obvious analogy between Joyal's combinatorial species and Goodwillie calculus?

A map of non-pathological topology?

What is the point of pointwise Kan extensions?

Does the category of (algebraically closed) fields of characteristic $p$ change when $p$ changes?

Is there a general theory of "compactification"?

What is the relationship between connective and nonconnective derived algebraic geometry?

Is there a rigid analytic geometry proof of the functional equation for the Riemann zeta function?

What was the error in the proof of Roos' theorem?

Converse to Stokes' Theorem

Why is the motivic category defined over the site of smooth schemes only?

Varieties where every algebra is free

Where's the best place for an algebraic geometer to learn some algebraic number theory?

What is the geometric significance of fibered category theory in topos theory?

Spectral sequences as deformation theory

Is every category a localization of a poset?

Does Con(ZF + Reinhardt) really imply Con(ZFC + I0)?

Are "most" spaces aspherical?

What are Koszul dualities?

What are _all_ of the exactness properties enjoyed by stable $\infty$-categories?

Why the stable module category?

What are some toy models for the stable homotopy groups of spheres?

What's with equivariant homotopy theory over a compact Lie group?

Why is Kan's $Ex^\infty$ functor useful?

Is algebraic $K$-theory a motivic spectrum?

Which $\ast$-algebras are $C^\ast$-algebras?