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Questions on group theory which concern finite groups.

4 votes

The automorphism of a group with a given fixed point set

A necessary condition is that $H $ be closed under any function $f $ that is equivariant under automorphisms $\sigma $ of $G $: $f(\sigma (x))=\sigma (f (x)) $ (and similarly for functions of several …
Bjørn Kjos-Hanssen's user avatar
2 votes

The finite subgroups of SU(n)

Just want to point out that an algorithm to answer, given $n$ and a presentation of a finite group $G$, whether $G$ is isomorphic to a finite subgroup of $SU(n)$, exists as a consequence of Tarski's T …
Bjørn Kjos-Hanssen's user avatar
7 votes
Accepted

The exceptional isomorphism between PGL(3,2) and PSL(2,7): geometric origin?

V. Dotsenko's construction, on math.stackexchange: https://math.stackexchange.com/questions/1401/why-psl-3-mathbb-f-2-cong-psl-2-mathbb-f-7/1450#1450 may fit your requirement "combinatorial mapping …
Bjørn Kjos-Hanssen's user avatar
13 votes
Accepted

Can any finite lattice be realized as an intermediate subgroups lattice?

This is an open problem. See Wikipedia article: http://en.m.wikipedia.org/wiki/Finite_lattice_representation_problem Palfy and Pudlak's result (see open-source description in Palfy's article Interva …
Bjørn Kjos-Hanssen's user avatar
20 votes
4 answers
2k views

Cayley graph of $A_5$ with generators $(1,2,3,4,5),(1,4,3,2,5)$

The Cayley graph of $A_5$ with two generators of order 5 seems rather complicated. What is its graph genus (orientable or non-orientable)? The best I could get by trial and error is an embedding wit …
Bjørn Kjos-Hanssen's user avatar