Journal of Operator Theory

Volume 35, Issue 1, Winter 1996 pp. 191-201.

On the stability of semi-Fredholm operators

Authors: Mostafa Mbekhta
Author institution:Université des Sciences et Technologies de Lille, U.R.A. D 751 CNRS “GAT”, U.F.R. de Mathématiques, F-59655 Villeneuve d’Ascq Cedex, FRANCE and Université de Galatasaray, Çiragan cad no. 102, Ortakoy, 80840 Istanbul, TURQUIE

Summary: We give some stability results for the “nullity” and “deficiency” of semi-Fredholm operators. We also give characterizations of the operators that are bounded from below (resp. surjective) in terms of the stability of the “nullity” (resp. the “deficiency”), as well as a generalization of the “punctured neighbourhood theorem”.

Keywords: Semi-Fredholm operator, s-regular, generalized kernel, generalized range, perturbation.

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