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Questions about the branch of algebra that deals with groups.
4
votes
2
answers
467
views
$H_2(H,\mathbb{Z})$ where $H$ is a f.g. normal subgroup of a f.p. group
Let $G$ be a finitely presented group and $H$ a finitely generated normal subgroup. Is it always true that the Schur Multiplier $H_2(H,\mathbb{Z})$ is a direct product of finitely generated abelian gr …
4
votes
1
answer
507
views
Quotients of the Higman Group
Chou asked in this paper whether The Higman group $H$ has a maximal normal subgroup $N$ such that $H/N$ has no (non-abelian) free subgroups (or is amenable). Is it known now if such subgroups exist …
5
votes
1
answer
228
views
Amenable groups with special presentations
Is there a group with a presentation
$\left< X \mid r_i, i \in \mathbb{N} \right>$ (where $X$ is finite) with
$\left< X \mid r_i, i \in A \right>$ is amenable
if and only if $A\subset \mathbb{N}$ …
12
votes
2
answers
816
views
Finitely generated subgroups with infinite cyclic quotient
Suppose that $G$ is a finitely presented group and $H$ is a finitely generated normal subgroup such that $G/H$ is infinite cyclic. Is it true that $H$ is finitely presented?
7
votes
0
answers
177
views
Countable elementary sub-structure of the automorphism group of the binary rooted tree
Let $G$ be the automorphism group of the binary rooted tree.
The downward Löwenheim-Skolem theorem states that G has a countable elementary sub-structure.
My question is whether such sub-structure i …
12
votes
1
answer
1k
views
Higman embedding theorem
The Higman Embedding theorem says that any finitely generated and recursively presented group can be embedded in a finitely presented group.
My question is if one can embed such a group as a normal s …
12
votes
5
answers
4k
views
What can be said about a group from its presentation?
This maybe a very general question.
If we have a group given by its presentation only, what kind of properties could be proven about it?
I know examples about non-amenability of some Burnside groups …
11
votes
0
answers
417
views
Topology of marked groups for different number of generators
A $k$-marked groups is a pair $(G,S)$ where $G$ is a group and $S$ is an ordered set of $k$ generators of $G$. Each such pair can be identified with a normal subgroup of the free group $F_k$ of rank $ …
7
votes
2
answers
240
views
Number of relations and free subgroups
Is there a function $f$ such that for any presentation $$G=\langle x_1,\ldots,x_n \mid r_1,\ldots,r_k\rangle\quad \text{with}\quad |r_i|\leq 3$$
$k\leq f(n)$ implies that $G$ has non-abelian free …
7
votes
Understanding groups that are not linear
If you have a finitely generated linear group whose growth is sub-exponential, then by
Tits alternative (mentioned above) the group has to be virtually solvable and by a theorem of Milnor the group h …
7
votes
1
answer
1k
views
Examples of finitely generated elementary amenable groups which are not virtually solvable
What are some examples of finitely generated (finitely presented) elementary amenable groups which are not virtually solvable?
1
vote
Accepted
Subgroups with Infinite cyclic quotients of the Thompons's group
The first answer is incomplete and moreover I suspect that it is incorrect!
Here is an answer submitted to me via email by Andrew Brunner, who asked me to post his answer for him since he is not sig …
3
votes
2
answers
372
views
Subgroups with Infinite cyclic quotients of the Thompons's group
A theorem in Geoghean's book is the following (theorem 18.3.18):
Let $G$ be a finitely presented group and let the rank of $G/G'$ (as
a $\mathbb{Z}$-module) be at least 2. If $G$ has no non-abelian …
10
votes
3
answers
1k
views
Profinite completion of a semidirect product
If we have two finitely generated residually finite groups $G$ and $H$, is there are relation between
the profinite completions $\hat{G},\hat{H}$ and the profinite completion of a semidirect
product …
8
votes
1
answer
529
views
Quotients of f.p. amenable groups
Can you give me an example of a finitely generated infinitely presented amenable group which is a quotient of a finitely presented amenable group?