Generalized weak demicompactness via perturbation and coperturbation functions

I. Ferjani

This paper focuses on studying the stability of generalized weakly demicompact operators on Banach spaces. To guarantee stability under strictly singular and cosingular perturbations, we introduce the notions of perturbation functions and coperturbation functions. Additionally, our results are applied to establish the invariance of the essential spectrum. 

Advanced Studies: Euro-Tbilisi Mathematical Journal, Vol. 18(1) (2025), pp. 111-120