Ruston elements and Fredholm theory

Abstract

We extend some of the Fredholm theory by, among other things, developing the  theory of Ruston and almost Ruston elements and spectra relative to an arbitrary homomorphism. In addition, we provide a number of applications and generalise certain well-known results.

Keywords: Fredholm, Weyl and Browder theory, Ruston and almost Ruston elements, exponential spectrum

Quaestiones Mathematicae 34(2011), 341–359