Purely Log Terminal Threefolds with Non-Normal Centres in Characteristic Two

Abstract

We show that many classical results of the minimal model program do not hold over an algebraically closed field of characteristic two. Indeed, we construct a three dimensional plt pair whose codimension one part is not normal, a three dimensional klt singularity which is not rational nor Cohen-Macaulay, and a klt Fano threefold with non-trivial intermediate cohomology.