On Almost Regular Mappings

TL;DR

This paper extends Ioffe's criterion to incomplete spaces with non-closed graphs, providing a new approach to regularity properties of set-valued mappings using an approximate Ekeland's variational principle.

Contribution

It introduces an analogue of Ioffe's criterion for almost openness in incomplete spaces with non-closed graphs, utilizing an approximate Ekeland's principle.

Findings

Derived an analogue of Ioffe's criterion for incomplete spaces.

Established stability of almost openness under perturbations.

Extended regularity analysis to non-closed graph mappings.

Abstract

Ioffe's criterion and various reformulations of it have become a~standard tool in proving theorems guaranteeing various regularity properties such as metric regularity, i.e., the openness with a linear rate around the reference point, of a~(set-valued) mapping. We derive an analogue of it guaranteeing the almost openness with a linear rate of mappings acting in incomplete spaces and having non-closed graphs, in general. The main tool used is an approximate version of Ekeland's variational principle for a function that is not necessarily lower semi-continuous and is defined on an abstract (possibly incomplete) space. Further, we focus on the stability of this property under additive single-valued and set-valued perturbations.