Isomorphisms of $AC(\sigma)$ spaces for countable sets

Abstract

It is known that the classical Banach--Stone theorem does not extend to the class of $AC(\sigma)$ spaces of absolutely continuous functions defined on compact subsets of the complex plane. On the other hand, if $\sigma$ is restricted to the set of compact polygons, then all the corresponding $AC(\sigma)$ spaces are isomorphic. In this paper we examine the case where $\sigma$ is the spectrum of a compact operator, and show that in this case one can obtain an infinite family of homeomorphic sets for which the corresponding function spaces are not isomorphic.Comment: 14 pages. Revised version with slightly expanded introduction. Some minor typos corrected. (To appear in the Proceedings of the 28th IWOTA, in "Operator Theory: Advances and Applications".