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Acta Mathematica Vietnamica

Variations of Weyl Type Theorems for Upper Triangular Operator Matrices

icon-email Mohammad H. M. Rashid

Abstract

Let X be a Banach space and let T be a bounded linear operator on X. We denote by S(T) the set of all complex λC such that T does not have the single-valued extension property. In this paper it is shown that if MC is a 2×2 upper triangular operator matrix acting on the Banach space XY, then the passage from σLD(A)σLD(B) to σLD(MC) is accomplished by removing certain open subsets of σd(A)σLD(B) from the former, that is, there is the equality σLD(A)σLD(B)=σLD(MC), where is the union of certain of the holes in σLD(MC) which happen to be subsets of σd(A)σLD(B). Generalized Weyl's theorem and generalized Browder's theorem are liable to fail for 2×2 operator matrices. In this paper, we also explore how generalized Weyl' theorem, generalized Browder's theorem, generalized a-Weyl's theorem and generalized a-Browder's theorem survive for 2×2 upper triangular operator matrices on the Banach space.