Separable reduction of Frechet subdifferentiability in Asplund spaces

Abstract

In the framework of Asplund spaces, we use two equivalent instruments - rich families and suitable models from logic - for performing separable reductions of various statements on Frechet subdifferentiability of functions. This way, isometrical results are actually obtained and several existed proofs are substantially simplified. Everything is based on a new structural characterization of Asplund spaces.