User Andreas Thom

61 votes

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How feasible is it to prove Kazhdan's property (T) by a computer?

answered May 21, 2014 at 16:30

54 votes

Are semi-direct products categorical (co)limits?

answered May 7, 2012 at 19:35

52 votes

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morphism from a compact group to Z ?

answered Nov 15, 2011 at 9:39

50 votes

Example for column rank $\neq$ row rank

answered Nov 25, 2010 at 20:33

42 votes

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Are there only countably many compact topological manifolds?

answered Feb 21, 2015 at 15:35

32 votes

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On the size of balls in Cayley graphs

answered Aug 19, 2010 at 21:53

30 votes

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Which finite groups have faithful complex irreducible representations?

answered Mar 2, 2011 at 17:02

27 votes

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products of conjugates in free groups

answered Apr 2, 2015 at 21:21

22 votes

Proofs that require fundamentally new ways of thinking

answered Dec 11, 2010 at 11:09

22 votes

‘Naturally occurring’ $K(\pi, n)$ spaces, for $n \geq 2$

answered Oct 29, 2010 at 6:12

21 votes

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Central Limit Theorem(s) for irrational rotation

answered Jun 30, 2014 at 15:55

20 votes

Is any connected fibre of a fibration of a sphere also a sphere?

answered Dec 7, 2014 at 13:29

20 votes

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Groups where word problem is solvable, but not quickly?

answered Aug 9, 2015 at 11:22

19 votes

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Can two rational rotations $F_2 = \langle A, B \rangle \to SO(3)$ efficiently approximate the $3 \times 3$ identity matrix?

answered Mar 30, 2016 at 16:17

18 votes

Properties of a non-sofic group

answered Oct 27, 2010 at 16:28

18 votes

Proofs that require fundamentally new ways of thinking

answered Dec 11, 2010 at 11:06

17 votes

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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 6:56

17 votes

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Is a map a homotopy equivalence if its suspension is so?

answered Nov 22, 2010 at 12:19

17 votes

No injective groups with more than one element?

answered Jun 21, 2012 at 15:20

17 votes

(Non)free differential calculus

answered Aug 25, 2011 at 18:17

16 votes

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contractible manifolds

answered Mar 30, 2011 at 20:05

16 votes

Discrete-compact duality for nonabelian groups

answered Jul 18, 2011 at 19:02

15 votes

Dehn's solution to Hilbert's 3rd: 1901 or 1902?

answered Aug 25, 2011 at 19:12

15 votes

Non-abelian Grothendieck group

answered Jan 7, 2015 at 20:21

15 votes

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Distributivity of group topologies on $\Bbb Z$

answered Nov 8, 2014 at 18:43

14 votes

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Solving equations in SO(3) : an open problem by Jan Mycielski

answered Jan 31, 2016 at 14:39

14 votes

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Centraliser of the complex conjugation in the absolute Galois group

answered Feb 7, 2013 at 15:44

14 votes

Is $SU(\infty)$ amenable?

answered Oct 17, 2011 at 17:23

14 votes

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Groups with large negative deficiency

answered Jan 26, 2011 at 19:37

14 votes

Is the group von Neumann algebra construction functorial?

answered Oct 8, 2010 at 21:32

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167 Answers

How feasible is it to prove Kazhdan's property (T) by a computer?

Are semi-direct products categorical (co)limits?

morphism from a compact group to Z ?

Example for column rank $\neq$ row rank

Are there only countably many compact topological manifolds?

On the size of balls in Cayley graphs

Which finite groups have faithful complex irreducible representations?

products of conjugates in free groups

Proofs that require fundamentally new ways of thinking

‘Naturally occurring’ $K(\pi, n)$ spaces, for $n \geq 2$

Central Limit Theorem(s) for irrational rotation

Is any connected fibre of a fibration of a sphere also a sphere?

Groups where word problem is solvable, but not quickly?

Can two rational rotations $F_2 = \langle A, B \rangle \to SO(3)$ efficiently approximate the $3 \times 3$ identity matrix?

Properties of a non-sofic group

Proofs that require fundamentally new ways of thinking

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

Is a map a homotopy equivalence if its suspension is so?

No injective groups with more than one element?

(Non)free differential calculus

contractible manifolds

Discrete-compact duality for nonabelian groups

Dehn's solution to Hilbert's 3rd: 1901 or 1902?

Non-abelian Grothendieck group

Distributivity of group topologies on $\Bbb Z$

Solving equations in SO(3) : an open problem by Jan Mycielski

Centraliser of the complex conjugation in the absolute Galois group

Is $SU(\infty)$ amenable?

Groups with large negative deficiency

Is the group von Neumann algebra construction functorial?