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Questions about the branch of algebra that deals with groups.

6 votes
3 answers
607 views

Action of $\pi_1(S)$ on its commutator subgroup

Let $G$ be a group. It acts canonically on its derived subgroup by conjugation. Can on describe the orbits of this action when $G$ is the fundamental group of a compact orientable surface of genus $g …
14 votes
3 answers
679 views

Compact manifolds with big mapping class group

I was wondering if compact surfaces were the only compact manifolds with a "big" or "complicated" mapping class group. Are there higher dimensional manifolds (which are not in some way reducible to …
1 vote
1 answer
432 views

Find a simple closed curve in $S$ which represents a commutator in $\pi_1 S$

I am interested in the following problem : decide if a certain element of the fundamental group can be represented by a simple closed curve. The general case has already been asked and answered on MO …
9 votes
1 answer
1k views

Fundamental group of an hyperbolic $4$-manifold

Good afternoon everyone, I have a very general question about hyperbolic manifolds and their fundamental groups in high dimension (at least $4$). If the theory of surfaces and $3$-manifolds provide …