Institut de Mathématiques de Jussieu, Équipe d'Analyse Fonctionnelle, Case 186, 4 place Jussieu, 75252 Paris Cedex 05, France ; University of Padova, Dipartimento di Matematica Pura ed Applicata, Via Belzoni 7, 35131 Padova, Italia
Abstract:
In this paper we characterize those functions of the real line to itself such that the nonlinear superposition operator defined by maps the Hölder-Zygmund space to itself, is continuous, and is times continuously differentiable. Our characterizations cover all cases in which is real and , and seem to be novel when is an integer.