Blocks of quotients of mackey algebras

Abstract

We review a theorem by Boltje and K¨ulshammer which states that under certain circumstances the endomorphism ring EndRG(RX) has only one block. We study the double Burnside ring, the Burnside ring and the transformations between two bases of it, namely the transitive G-set basis and the primitive idempotent basis. We introduce algebras Λ, Λdef and Υ which are quotient algebras of the inflation Mackey algebra, the deflation Mackey algebra and the ordinary Mackey algebra respectively. We examine the primitive idempotents of Z(Υ). We prove that the algebra Λ has a unique block and give an example where Λdef has two blocks.