Semi-Fredholm operators with finite ascent or descent and perturbations

Rakočević, Vladimir

doi:10.1090/S0002-9939-1995-1286004-6

Semi-Fredholm operators with finite ascent or descent and perturbations
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by Vladimir Rakočević

Proc. Amer. Math. Soc. 123 (1995), 3823-3825

DOI: https://doi.org/10.1090/S0002-9939-1995-1286004-6

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Abstract:

In this note we prove that the collection of upper (lower) semi-Fredholm operators with finite ascent (descent) is closed under commuting operator perturbations that belong to the perturbation class associated with the set of upper (lower) semi-Fredholm operators. Then, as a corollary we get the main result of S. Grabiner (Proc. Amer. Math. Soc. 71 (1978), 79-80).

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