## Topology & Geometric Group Theory Seminar

## Spring 2008

### 1:30 - 2:30, Malott 207

Tuesday, February 12

**José
Burillo**, Universitat Politécnica de Catalunya

*Commensurators and finite-index subgroups of Thompson's group F
*

In this talk we will give a complete description of the abstract
commensurator of Thompson's group F, and we will prove that it embeds in
the quasi-isometry group of F, hence providing a large number of examples
of quasi-isometries of F. As a corollary of this result, we classify all
finite-index subgroups of F, proving that they are all virtually F, and
identifying exactly those which are isomorphic to F itself. (Joint work
with Sean Cleary and Claas Röver).

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