## Olivetti Club

Chaitanya Tappu
Arbres, amalgames and possibly $\mathrm {SL}_2$
Tuesday, October 29, 2019 - 4:30pm
Malott 406

A graph of groups construction is a generalisation of free products of groups, and it also generalises another construction called an HNN extension. The topological viewpoint gives rise to an action of the constructed group on a tree, and conversely a group action on a tree leads to a graph of groups. This theory was developed by Jean-Pierre Serre and Hyman Bass to study some linear algebraic groups in J-P Serre's monograph Arbres, amalgames, $\mathrm {SL}_2$' (title of the English translation: Trees'), but quickly became a standard tool in geometric topology and geometric group theory.
In this talk, I will present the correspondence between graphs of groups and groups acting on trees.

Refreshments will be served in the lounge at 4:00 PM.