A topological and geometric approach to fixed points results for sum of operators and applications

In this paper, we establish a fixed point result of Krasnoselskii type for the sum A + B, where A and B are continuous maps acting on locally convex spaces. Our results extend previous ones. We apply such results to obtain strong solutions for some quasi-linear elliptic equations with lack of compactness. We also provide an application to the existence and regularity theory of solutions to a nonlinear integral equation modeled in a Banach space. In the last section we develop a sequentially weak continuity result for a class of operators acting on vector-valued Lebesgue spaces. Such a result is used together with a geometric condition as the main tool to provide an existence theory for nonlinear integral equations in L-p(E). (C) 2004 Elsevier Ltd. All rights reserved.