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Proyecciones (Antofagasta)

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KARMOUNI, M.; TAJMOUATI, A.  and  BAKKALI, A. El. Upper triangular operator matrices and limit points of the essential spectrum. Proyecciones (Antofagasta) [online]. 2019, vol.38, n.3, pp.401-409. ISSN 0716-0917.

In this paper, we investigate the limit points set of essential spectrum of upper triangular operator matrices

We prove that accσe(MC) ∪ W = accσe(A) ∪ accσe(B) where W is the union of certain holes in accσe(MC), which happen to be subsets of accσe(B) ∩ accσe(A). Also, several sufficient conditions for accσe(MC) = accσe(A) ∪ accσe(B) holds are given.

Keywords : Fredholm operator; Essential spectra; Limit point; Operator matrices.; 47A10; 47A11.

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