Perturbation results for Weyl type theorems
Acta mathematica Universitatis Comenianae, Tome 80 (2011) no. 1
M. Berkani; H. Zariouh. Perturbation results for Weyl type theorems. Acta mathematica Universitatis Comenianae, Tome 80 (2011) no. 1. http://geodesic.mathdoc.fr/item/AMUC_2011_80_1_a9/
@article{AMUC_2011_80_1_a9,
     author = {M. Berkani and H. Zariouh},
     title = {Perturbation results for {Weyl} type theorems},
     journal = {Acta mathematica Universitatis Comenianae},
     year = {2011},
     volume = {80},
     number = {1},
     url = {http://geodesic.mathdoc.fr/item/AMUC_2011_80_1_a9/}
}
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JO  - Acta mathematica Universitatis Comenianae
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%J Acta mathematica Universitatis Comenianae
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In [12] we introduced and studied properties ( gab ) and ( gaw ), which are extensions to the context of B-Fredholm theory, of properties ( ab ) and ( aw ) respectively introduced also in [12]. In this paper we continue the study of these properties and we consider their stability under commuting finite rank, compact and nilpotent perturbations. Among other results, we prove that if T is a bounded linear operator acting on a Banach space X , then T possesses property ( gaw ) if and only if T satisfies generalized Weyl's theorem and E ( T ) = Ea ( T ). We prove also that if T possesses property ab or property ( aw ) or property ( gaw ) respectively, and N is a nilpotent operator commuting with T , then T+N possesses property ab or property aw or property ( gaw ) respectively. The same result holds for property ( gab ) in the case of a-polaroid operators.