On the separability of the restriction functor

Abstract

Let G be a group, Λ = L σ∈G Λσ a strongly graded ring by G, H a subgroup of G and ΛH = L σ∈H Λσ. We give a necessary and sufficient condition for the ring Λ/ΛH to be separable, generalizing the corresponding result for the ring extension Λ/Λ1. As a consequence of this result we give a condition for Λ to be a hereditary order in case Λ is a strongly graded by finite group R-order in a separable K-algebra, for R a Dedekind domain with quotient field K.