
Journal of Convex Analysis 30 (2023), No. 3, 771792 Copyright Heldermann Verlag 2023 A Quest for Simple and Unified Proofs in Regularity Theory: Perturbation Stability Radek Cibulka NTIS  New Technologies for the Information Society, and: Department of Mathematics, Faculty of Applied Sciences,, University of West Bohemia, Plzen, Czech Republic cibi@kma.zcu.cz Tomás Roubal NTIS  New Technologies for the Information Society, and: Department of Mathematics, Faculty of Applied Sciences,, University of West Bohemia, Plzen, Czech Republic roubalt@kma.zcu.cz Ioffe's criterion and various reformulations of it have become a~standard tool in proving theorems guaranteeing metric regularity of a (setvalued) mapping. First, we demonstrate that one should always use directly the socalled general criterion which follows, for example, from Ekeland's variational principle, and that there is no need to make a detour through the slopebased consequences of this general statement. Second, we argue that when proving perturbation stability results, in the spirit of LyusternikGraves theorem, there is no need to employ the concept of a lower semicontinuous envelope even in the case of an incomplete target space. The gist is to use the "correct" function to which Ekeland's variational principle is applied; namely, the distance function to the graph of the setvalued mapping under consideration. This approach originates in the notion of graphical regularity introduced by L. Thibault, which is equivalent to the property of metric regularity. Our criteria cover also both metric subregularity and metric semiregularity, which are weaker properties obtained by fixing one of the points in the definition of metric regularity. Keywords: Metric regularity, graphical regularity, Ioffe criterion, perturbation stability. MSC: 47J05 47J07 49J52 49J53 58C15. [ Fulltextpdf (179 KB)] for subscribers only. 