• Chaker, Wajdi (Department of New Economy University of Sfax Higher Institute of Comercial Studies of Sfax) ;
  • Jeribi, Aref (Department of Mathematics University of Sfax Faculty of Sciences of Sfax) ;
  • Krichen, Bilel (Department of Mathematics University of Sfax Faculty of Sciences of Sfax)
  • Received : 2020.06.25
  • Accepted : 2020.11.19
  • Published : 2021.04.30


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.


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