%0 Journal Article %T Descriptive set theoretic methods applied to strictly singular and strictly cosingular operators %A G. Androulakis %A K. Beanland %J Mathematics %D 2008 %I arXiv %X The class of strictly singular operators originating from the dual of a separable Banach space is written as an increasing union of $\omega_1$ 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. %U http://arxiv.org/abs/0806.0056v1