Geometry Topology Student Seminar
Wednesday, September 5, 2012 - 2:00pm
1 hour (actually 50 minutes)
The main goal is to characterize the dilatation of an outer automorphisms of free groups. It is known that for any automorphism, its dilatation is a weak Perron number. The converse was recently shown by Thurston; for every weak Perron number, there is an automorphism represented by a train track map. We will discuss Thurston's theorem and its proof.