Purity reconsidered

Abstract

Talk in the conference:The Cohomology of Moduli SpacesOrganized by Gerard van der Geer and Carel FaberAmsterdam, 16-20 XII 2002Convention: all base schemes will be in characteristic p. Writing k or Ω we will assumek=k Fp respectively Ω=Ω Fp We will write X ->S for a p divisible group over a baseS(and sometimes will say a family of pdivisible groups),while we tend to write X whenwe consider a p divisible group over a base field (but we are not strict in this convention)Instead of p divisible group one can also use the equivalent notion Barsotti Tate group