Upper triangular operator matrices and limit points of the essential spectrum
Keywords:Fredholm operator, Essential spectra, Limit point, Operator matrices
AbstractIn this paper, we investigate the limit points set of essential spectrum of upper triangular operator matrices We prove that acc?e(MC) ? W = acc?e(A) ? acc?e(B) where W is the union of certain holes in acc?e(MC), which happen to be subsets of acc?e(B) ? acc?e(A). Also, several sufficient conditions for acc?e(MC) = acc?e(A) ? acc?e(B) holds are given.
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