Generalized Drazin spectrum of operator matrices

Let A ∈ B(X) and B ∈ B(Y), MC be an operator on Banach space X ⊕ Y given A C by MC =A generalized Drazin spectrum defined by σgD(T) = {λ∈ C : T-0 BλI is not generalized Drazin invertible} is considered in this paperIt is shown thatσgD(A) ∪σgD(B) = σgD(MC) ∪ WgD(A, B, C),where WgD(A, B, C) is a subset of σgD(A) ∩σgD(B) and a union of certain holes in σgD(MC).Furthermore, several sufficient conditions for σgD(A) ∪σgD(B) = σgD(MC) holds for every C ∈ B(Y, X) are given.