Division ring extensions and a counterexample to the pure semisimplicity conjecture

Abstract

We construct a family of division ring extensions and compute their left and right dimensions. In characteristic zero, we obtain a counterexample to the pure semisimplicity conjecture: a hereditary right pure semisimple ring of infinite representation type. For each prime $p\ge3$, we construct in characteristic $p$ a hereditary artinian ring of finite representation type with Coxeter diagram $I_2(p+2)$.