
Piotr Przytycki
McGill University
Title
Trees, fixed points, and the Cremona group
Abstract
An action of a group on a space is called decent if every finitely generated subgroup all of whose elements have fixed-points has a global fixed-point. An example is the automorphism group of a tree or a finite product of trees. I will give a sufficient condition for a group acting on a restricted infinite product of trees to be decent. This allows to prove that every finitely generated subgroup of the Cremona group of P2 all of whose elements are algebraic is bounded. Joint work with Anne Lonjou and Christian Urech.