Ultrametric Spaces and Logic Programming

Abstract In this paper we prove a very general multivalued fixed point theorem for ultrametric spaces which at the same time is a generalization of the multivalued fixed point theorem of Khamsi et al. for generalized metric spaces and our (singlevalued) fixed point theorem for ultrametric spaces. We use this latter fixed point theorem to obtain a criterion for the existence of a Herbrand model for a program.