Descriptive Set Theoretic Methods Applied to Strictly Singular and Strictly Cosingular Operators

Abstract

The class of strictly singular operators originating from the dual of a separable Banach space is written as an increasing union of ω ₁ subclasses which are defined using the Schreier sets. A question of J. Diestel, of whether a similar result can be stated for strictly cosingular operators, is studied.