Mark Kisin Universität Munster Equivariant Poincare polynomials and counting points in characteristic p. Friday 11th, April 12:05-12:55pm, Stephen Roberts. Let M0,n be the moduli spaceparametrising ordered n-tuples of points on the complex sphere. I will explain joint work with Gus Lehrer in which we compute the action of the symmetric group Sn on the cohomology of M0,n. The proof exploits a connection - going back to Andre Weil - between the topology of varieties in characteristic p, and their arithmetic in positive characteristic.