Clifford theory for Mackey algebras

We develop a Clifford theory for Mackey algebras. For simple Mackey functors, using their classification we prove Mackey algebra versions of Clifford's theorem and the Clifford correspondence. Let μ_R (G) be the Mackey algebra of a finite group G over a commutative unital ring R, and let 1_N be the unity of μ_R (N) where N is a normal subgroup of G. Observing that 1_N μ_R (G) 1_N is a crossed product of G / N over μ_R (N), a number of results concerning group graded algebras are extended to the context of Mackey algebras, including Fong's theorem, Green's indecomposibility theorem and some reduction and extension techniques for indecomposable Mackey functors.