Sergey Shpectorov: Amalgams and their completions



As far as group-theoretic background, "Finite group theory" of Aschbacher covers most of my needs. The following topics deserve special attention.

1. Classical groups: this will be the source of most examples.

Additionally, I can recommend "The geometry of the classical groups" by Taylor.

2. 1st and 2nd cohomology groups and their implications for the group extensions. Schur multiplier.

3. Amalgams, free groups, free products of groups.

"Trees" by Serre is a classical source.