Ordinary Grothendieck groups of a Frobenius P-category (1004.1615v1)

Abstract: In "Frobenius Categories versus Brauer Blocks", Progress in Math. 274, we have introduced the Frobenius categories F over a finite p-group P, and we have associated to F - suitably endowed with some central k*-extensions - a "Grothendieck group" as an inverse limit of Grothendieck groups of categories of modules in characteristic p obtained from F, determining its rank. Our purpose here is to introduce an analogous inverse limit of Grothendieck groups of categories of modules in characteristic zero obtained from F, determining its rank and proving that its extension to a field is canonically isomorphic to the direct sum of the corresponding extensions of the "Grothendieck groups" above associated with the centralizers in F of a suitable set of representatives of the F-classes of elements of P.