Alexandra Pettet, 3 juin 2008, 11h15, MA 12

Abstract:

The well-rounded retract of SL_n(Z), first described by Soule, Lannes, and Ash, is an equivariant deformation retract of the associated symmetric space, having minimal dimension, the virtual cohomlogical dimension of SL_n(Z). We prove that the well-rounded retract is minimal in the sense that it contains no proper, closed, contractible, invariant subsets. This is joint work with Juan Souto.