User Colin Reid

35 votes

2 answers

1k views

Why do sporadic simple groups have so few conjugacy classes?

asked Dec 14, 2014 at 23:46

20 votes

5 answers

2k views

Estimate for the order of the outer automorphism group of a finite simple group

asked Apr 9, 2010 at 12:47

13 votes

1 answer

2k views

Topologies on an infinite symmetric group

asked Feb 17, 2010 at 16:19

11 votes

1 answer

638 views

Is every finite group a proper quotient of a finite primitive group?

asked Mar 7, 2011 at 19:59

10 votes

2 answers

2k views

pro-discrete = locally compact and open normal subgroups have trivial intersection?

asked Oct 18, 2010 at 19:04

9 votes

2 answers

669 views

Vigorous actions on the Cantor set

asked Dec 16, 2011 at 12:15

9 votes

0 answers

329 views

'Infinitesimal' elements of a topological group

asked Mar 22, 2012 at 17:37

9 votes

3 answers

865 views

Recognising group actions on trees from the boundary

asked May 18, 2012 at 12:57

8 votes

1 answer

854 views

Largest possible order of a nilpotent permutation group?

asked Feb 18, 2010 at 13:34

7 votes

1 answer

207 views

Hausdorff dimension of products of normal subgroups

asked Sep 2, 2010 at 16:17

7 votes

0 answers

419 views

Strange normal subgroups of profinite groups

asked Sep 4, 2012 at 8:34

6 votes

0 answers

293 views

Examples of a non-Hopfian phenomenon in group theory

asked Feb 10, 2012 at 12:05

6 votes

5 answers

440 views

Antichains and measure-preserving actions on Boolean algebras

asked Sep 26, 2011 at 13:27

6 votes

1 answer

1k views

subgroups of the direct product intersecting trivially with the direct sum

asked Jan 27, 2011 at 15:57

6 votes

1 answer

144 views

Continuity of conjugation actions of Polish groups

asked May 12, 2015 at 6:46

5 votes

1 answer

163 views

Characteristically simple locally compact abelian groups

asked Apr 23, 2016 at 2:54

5 votes

1 answer

169 views

Furstenberg decomposition for non-compact spaces

asked Mar 2, 2017 at 2:53

5 votes

0 answers

107 views

A dynamical property of automorphisms of a locally compact group

asked Sep 14, 2012 at 4:47

5 votes

0 answers

93 views

Separation of topological group elements by invariant neighbourhooods

asked Jul 14, 2014 at 9:36

5 votes

1 answer

170 views

Equations and random subgroups in compact groups

asked Aug 14, 2014 at 4:50

4 votes

0 answers

275 views

Interesting commensurated subgroups of countable groups

asked Aug 20, 2012 at 2:19

4 votes

3 answers

395 views

A characterisation of Boolean algebras

asked Aug 30, 2012 at 0:00

4 votes

2 answers

1k views

Supermartingales and convergence

asked Feb 17, 2011 at 14:45

4 votes

0 answers

841 views

Isomorphism types of subnormal subgroups

asked Nov 22, 2010 at 19:02

4 votes

1 answer

440 views

Centralisers of transitive permutation groups

asked Oct 4, 2010 at 10:33

4 votes

1 answer

288 views

Can a soluble group compute OR?

asked Oct 6, 2010 at 16:11

4 votes

2 answers

462 views

Distinguishing finite-orbit permutation groups by action on tuples

asked Sep 3, 2010 at 16:46

4 votes

1 answer

147 views

Equicontinuity and orbits of compact open sets

asked Jul 7, 2017 at 8:57

4 votes

0 answers

90 views

Is there a name for this kind of structure? (Not quite a lattice-ordered group)

asked Sep 8, 2018 at 15:39

4 votes

0 answers

98 views

Subgroup complemented by a double coset of a non-maximal subgroup

asked Jan 22, 2022 at 6:45

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50 Questions

Why do sporadic simple groups have so few conjugacy classes?

Estimate for the order of the outer automorphism group of a finite simple group

Topologies on an infinite symmetric group

Is every finite group a proper quotient of a finite primitive group?

pro-discrete = locally compact and open normal subgroups have trivial intersection?

Vigorous actions on the Cantor set

'Infinitesimal' elements of a topological group

Recognising group actions on trees from the boundary

Largest possible order of a nilpotent permutation group?

Hausdorff dimension of products of normal subgroups

Strange normal subgroups of profinite groups

Examples of a non-Hopfian phenomenon in group theory

Antichains and measure-preserving actions on Boolean algebras

subgroups of the direct product intersecting trivially with the direct sum

Continuity of conjugation actions of Polish groups

Characteristically simple locally compact abelian groups

Furstenberg decomposition for non-compact spaces

A dynamical property of automorphisms of a locally compact group

Separation of topological group elements by invariant neighbourhooods

Equations and random subgroups in compact groups

Interesting commensurated subgroups of countable groups

A characterisation of Boolean algebras

Supermartingales and convergence

Isomorphism types of subnormal subgroups

Centralisers of transitive permutation groups

Can a soluble group compute OR?

Distinguishing finite-orbit permutation groups by action on tuples

Equicontinuity and orbits of compact open sets

Is there a name for this kind of structure? (Not quite a lattice-ordered group)

Subgroup complemented by a double coset of a non-maximal subgroup