The Perturbation Classes Problem for Closed Operators

Pietro Aiena, Muneo Cho, Manuel Gonzalez


We compare the perturbation classes for closed semi-Fredholm and Fredholm operators
with dense domain acting between Banach spaces with the corresponding perturbation
classes for bounded semi-Fredholm and Fredholm operators.
We show that they coincide in some cases, but they are different in general.
We describe several relevant examples and point out some open problems.

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