The Variable Radius Form of the Extended Exterior Sphere Condition

Journal of Convex Analysis (2025) We introduce a variable radius form of the extended exterior sphere condition of [16], and then, we prove that the complement of a closed set satisfying this new property is nothing but the union of closed balls with lower semicontinous radius function. This generalizes, to the variable radius case, the main result of [16], namely, [16, Theorem 1.2]. On the other hand, as it is shown in [14,15] for prox-regularity, the exterior sphere condition, and the union of closed balls property, we prove that the constant and the variable radius forms of the extended exterior sphere condition belong to the S-convexity regularity class.