Some Fredholm theory results around relative demicompactness concept

Wajdi Chaker; Aref Jeribi; Bilel Krichen

doi:10.4134/CKMS.c200215

Communications of the
Korean Mathematical Society CKMS

ISSN(Print) 1225-1763 ISSN(Online) 2234-3024

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Commun. Korean Math. Soc. 2021; 36(2): 313-325

Online first article December 11, 2020 Printed April 30, 2021

https://doi.org/10.4134/CKMS.c200215

Some Fredholm theory results around relative demicompactness concept

Wajdi Chaker, Aref Jeribi, Bilel Krichen

Higher Institute of Comercial Studies of Sfax; Faculty of Sciences of Sfax; Faculty of Sciences of Sfax

Abstract

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Abstract

In this paper, we provide a characterization of upper semi-Fredholm operators via the relative demicompactness concept. The obtained results are used to investigate the stability of various essential spectra of closed linear operators under perturbations belonging to classes involving demicompact, as well as, relative demicompact operators.

Keywords: Fredholm theory, demicompact operator, essential spectrum

MSC numbers: Primary 47A10; Secondary 47A55, 47A53