An intersection theorem for set-valued mappings

Abstract

Given a nonempty convex set X in a locally convex Hausdorff topological vector space, a nonempty set Y and two set-valued mappings T: X a double dagger parts per thousand X, S: Y a double dagger parts per thousand X we prove that under suitable conditions one can find an x a X which is simultaneously a fixed point for T and a common point for the family of values of S. Applying our intersection theorem, we establish a common fixed point theorem, a saddle point theorem, as well as existence results for the solutions of some equilibrium and complementarity problems.