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Questions about the branch of algebra that deals with groups.
7
votes
Accepted
A finitely presented group with two simple relations
The group $G$ is not solvable, since its quotient
$$
\tilde{G} := \langle x, y \ | \ x^7 = 1, y^2xy = x^4, y^{15} = 1\rangle
$$
is a group of order $423360$ such that $\tilde{G}'' \cong {\rm PSL}(3, …
3
votes
Accepted
Example of a group in which centralizers of every element are non-abelian
The smallest groups in which the centralizer of every element is non-abelian
have order $32$. You can find them with GAP as follows:
gap> IsExample := G -> ForAll(ConjugacyClasses(G),
> …
7
votes
Accepted
Structure of the group generated by two specific symplectic matrices
Your representation $p$ is not faithful, since we have
$$
(ABA^{-1}BA^{-1}BAB^{-1})^3 \ = \ 1.
$$
In particular, this means that
$$
(aba^{-1}ba^{-1}bab^{-1})^3 \ = \
\left(\begin{array}{rr}%
- …
10
votes
Finite groups with elements of the same order
The smallest counterexamples have order $16$.
Up to isomorphism, there are $14$ groups of order $16$;
these fall into $9$ distinct equivalence classes w.r.t. order portrait.
The $3$ equivalence classe …
1
vote
Accepted
Properties of a special finitely presented groups
Your group $G$ is not solvable since it has a quotient isomorphic
to ${\rm S}_5$. You can see this with GAP as follows:
gap> F := FreeGroup("a","b","c");
<free group on the generators [ a, b, c ]>
ga …
12
votes
Ore's Conjecture for perfect groups
The counterexample described by Derek Holt can easily be checked with GAP
as follows:
gap> G := Image(IsomorphismPermGroup(PerfectGroup(960,2)));
A5 2^4'
gap> CommutatorLength(G); # > 1 => there are …
3
votes
2
answers
402
views
Classes of finitely generated groups for which it is known whether they contain periodic groups
Question: For which "interesting" classes of finitely generated groups is
it known whether every infinite group in the class has an element of infinite order?
Some examples:
For finitely gen …
6
votes
Accepted
How large can abelian subgroups of class 2 nilpotent groups or simple groups be?
The answer to both questions is no:
Counterexample to first assertion: $G = {\rm A}_5$, $H = \langle (1,2,3,4,5) \rangle$.
Counterexample to second assertion: $G = \langle (1,2,3,4), (1,3), (5,6) \r …
8
votes
Accepted
Notation of Wilson's book "The finite simple groups"
I don't have the book at hand, but I think the usual meaning of $G = A.B$ for groups $A$ and $B$ is that $G$ has a normal subgroup isomorphic to $A$ such that the quotient $G/A$ is isomorphic to $B$. …
2
votes
Metacyclic groups in $AGL(4,3)$
There are no such groups.
With GAP one can check this as follows:
Construct the group $G := {\rm AGL}(4,3)$:
gap> G := SemidirectProduct(GL(4,3),GF(3)^4);
<matrix group of size 1965150720 with 3 gen …
4
votes
wreath product and matrix presentation
You can obtain an embedding of $H$ into ${\rm GL}(2^r,\mathbb{Z})$ as follows:
Given a positive integer $m$, put
$$
A_m \ := \
\left(
\begin{array}{ll}
0 & 1_m \\\
1_m & 0
\ …
5
votes
Are residually finite, perfect groups residually alternating?
If you allow the group to be finite, any non-alternating finite simple group
is a counterexample. Otherwise you can still obtain counterexamples from
wreath products of such groups with the infinite c …
2
votes
Can finitely generated subgroups of limit groups be detected in free group quotients?
Meanwhile there is a paper which specifically refers to this MathOverflow question, and which in particular shows that in general, limit groups are not freely subgroup separable:
Simon Heil, JSJ decom …
11
votes
1
answer
496
views
Numbers of distinct products obtained by permuting 3 factors
Let $G$ be a group, and assume that there exist $a, b, c \in G$ such that
$abc$, $acb$, $bac$, $bca$, $cab$ and $cba$ are precisely 5 distinct elements
(i.e. that precisely two of the products are equ …
9
votes
0
answers
398
views
'Almost-isomorphic' groups
What can be said about pairs of non-isomorphic groups which are epimorphic images of one another and which also embed into one another?
Can such pairs of groups be 'classified' in some sufficiently w …