Author

Lo Quang Chu

Date of Award

1977

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mathematics

Supervisor

T. Husain

Abstract

It is a well-known result of I.C. Gohberg, M.G. Krein and T. Kato that if T is a semi-Fredholm operator between Banach spaces and P a bounded operator of norm small enough, or a compact operator, then T+P is a semi-Fredholm operator with the same index as T.

This thesis is concerned with extensions of this result to more general locally made of suitably defined small bounded or precompact perturbations or Φ₊ and Φ₋ -operators. The results obtained apply in particular to Frechet spaces and effectively extend the theorems of I.C. Gohberg, M.G. Krein and T. Kata as well as several or Ju.M. Vladimirski.

Duality is shown to be a convenient tool to prove many or these results. Some applications are also given.



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