Xiao Hong CAO
When A∈B(H1), B∈B(H2) and C∈B(H3) are given, we denote by M(D,E,F) an operator, acting on the Hilbert space H1H2H3, of the form M(D, E, F)= . In this paper, we give the necessary and sufficient condition for M(D,E,F) to be upper semi-Fredholm (lower semi-Fredholm) operator for some D∈B(H2,H1), E∈B(H3,H1), F∈B(H3,H2). Weyl type theorems are liable to fail for 2×2 operator matrices. In this paper, we also explore how Weyl's theorem, Browder's theorem, α-Weyl's theorem and α-Browder's theorem survive for 3×3 upper triangular operator matrices on the Hilbert space.