User Torsten Ekedahl

55 votes

Why worry about the axiom of choice?

answered Apr 29, 2010 at 5:46

51 votes

Accepted

Separable and algebraic closures?

answered Jun 7, 2010 at 8:47

43 votes

Accepted

From Zeta Functions to Curves

answered Jul 18, 2011 at 10:01

34 votes

Accepted

Which groups have only real and quaternionic irreducible representations?

answered Nov 27, 2010 at 11:34

30 votes

Is there a machinery describing all the irreducible representations ?

answered Mar 18, 2010 at 16:20

29 votes

Accepted

What do coherent topoi have to do with completeness?

answered Jun 21, 2011 at 5:46

28 votes

Accepted

Why are normal crossing divisors nice?

answered May 6, 2010 at 19:57

28 votes

Symmetric powers and duals of vector bundles in char p

answered Aug 4, 2010 at 13:21

26 votes

Accepted

Which 'well-known' algebraic geometric results do not hold in characteristic 2?

answered Jul 6, 2011 at 20:24

25 votes

Accepted

How does Tate verify his own conjecture for the Fermat hypersurface?

answered May 13, 2011 at 4:56

23 votes

The role of completeness in Hilbert Spaces

answered Aug 17, 2010 at 6:31

23 votes

Why does the Grothendieck group $K_0(R)$ of a ring not depend on our choice of using left modules instead of right modules?

answered Nov 19, 2010 at 12:06

22 votes

What algebraic group does Tannaka-Krein reconstruct when fed the category of modules of a non-algebraic Lie algebra?

answered Apr 15, 2010 at 13:27

22 votes

"Largest" finite-dimensional Lie subgroups of Diff(S^n), are they known?

answered Jun 13, 2010 at 19:11

22 votes

What about stacks of categories in algebraic geometry?

answered Mar 1, 2011 at 6:33

21 votes

Is it true that if $\operatorname{Ext}^{1}_{A}(P,A/I)=0 $ for all $ I$ then $P$ is projective?

answered May 23, 2010 at 17:41

21 votes

Orbit structures of conjugacy class set and irreducible representation set under automorphism group

answered Apr 17, 2010 at 6:35

21 votes

Automorphism group of a scheme

answered Feb 10, 2011 at 19:08

21 votes

Accepted

Chevalley–Shephard–Todd theorem

answered Jul 19, 2010 at 7:33

20 votes

Accepted

What is the wild fundamental group?

answered Jan 18, 2011 at 7:27

20 votes

Accepted

Is $Sym^n (V^*) \cong Sym^n (V)^\ast$ naturally in positive characteristic?

answered Feb 15, 2010 at 16:59

20 votes

extensions, abelian varieties, $\mathbb{G}_m$

answered May 10, 2011 at 5:41

19 votes

What are some fundamental "sources" for the appearance of pi in mathematics?

answered Mar 14, 2010 at 17:43

19 votes

Examples of eventual counterexamples

answered Jun 12, 2010 at 18:52

19 votes

Accepted

Hilbert 90 for algebras

answered Jun 17, 2010 at 8:30

19 votes

Accepted

Analogue of Smith normal form for matrices over $\mathbb Z[t]$

answered Jan 13, 2011 at 13:54

19 votes

Accepted

Motivic characterization of affine spaces

answered Oct 17, 2010 at 14:21

18 votes

About isogeny theorem for elliptic curves

answered Oct 12, 2010 at 19:33

18 votes

Accepted

Suzuki and Ree groups, from the algebraic group standpoint

answered Jul 29, 2010 at 20:35

17 votes

Torsors for finite group schemes

answered Nov 20, 2010 at 7:35

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203 Answers

Why worry about the axiom of choice?

Separable and algebraic closures?

From Zeta Functions to Curves

Which groups have only real and quaternionic irreducible representations?

Is there a machinery describing all the irreducible representations ?

What do coherent topoi have to do with completeness?

Why are normal crossing divisors nice?

Symmetric powers and duals of vector bundles in char p

Which 'well-known' algebraic geometric results do not hold in characteristic 2?

How does Tate verify his own conjecture for the Fermat hypersurface?

The role of completeness in Hilbert Spaces

Why does the Grothendieck group $K_0(R)$ of a ring not depend on our choice of using left modules instead of right modules?

What algebraic group does Tannaka-Krein reconstruct when fed the category of modules of a non-algebraic Lie algebra?

"Largest" finite-dimensional Lie subgroups of Diff(S^n), are they known?

What about stacks of categories in algebraic geometry?

Is it true that if $\operatorname{Ext}^{1}_{A}(P,A/I)=0 $ for all $ I$ then $P$ is projective?

Orbit structures of conjugacy class set and irreducible representation set under automorphism group

Automorphism group of a scheme

Chevalley–Shephard–Todd theorem

What is the wild fundamental group?

Is $Sym^n (V^*) \cong Sym^n (V)^\ast$ naturally in positive characteristic?

extensions, abelian varieties, $\mathbb{G}_m$

What are some fundamental "sources" for the appearance of pi in mathematics?

Examples of eventual counterexamples

Hilbert 90 for algebras

Analogue of Smith normal form for matrices over $\mathbb Z[t]$

Motivic characterization of affine spaces

About isogeny theorem for elliptic curves

Suzuki and Ree groups, from the algebraic group standpoint

Torsors for finite group schemes