Preservation of the Existence of Zeros in a Family of Set-Valued Functionals and Some Consequences

Abstract

A theorem on the preservation of the existence of zeros under the change of the parameter in a one-parameter family of $$(\alpha,\beta)$$ -search functionals on an open subset of a metric space is proved. The following corollaries of this theorem are presented: on the preservation of the existence of preimages of a given closed subspace in a parametric family of multivalued mappings of metric spaces; on the preservation of the existence of coincidence points in a finite collection of two or more families of multivalued mappings of metric spaces; on the preservation of the existence of common fixed points in a collection of families of multivalued mappings to itself of a metric space. As a simple particular case, the Frigon–Granas theorem (1994) on fixed points of a contraction family of multivalued mappings is obtained.