On Generalized Schur's Lemma and Its Applications

Abstract

In this paper, we generalize Schur's lemma on the basis of endomorphism rings for permutation modules. Let H be a subgroup of G and let M be a module of H. Set N = NG(H). Then there is a natural embedding of End N(MN) into End G(MG). By taking H to be a p-subgroup of G, we can reformulate Green's theory on modular representation. A defect theory is defined on the endomorphism ring of any induced module and it is used to prove Green's correspondence and related results. This defect theory can unify some well known results in modular representation theory. By using generalized Schur's lemma, we can also give a method to determine the multiplicity of simple modules in any permutation module of symmetric groups. This makes it possible to prove various versions of Foulkes' conjecture in a uniform way.