The complement of a closed set satisfying the extended exterior sphere condition
摘要
We provide a novel analytical proof of an improved version of Nour and Takche (J Convex Anal, 2025, Theorem 3.1), showing that the complement of a closed set satisfying the extended exterior sphere condition is nothing but the union of closed balls with lower semicontinuous radius function. The improvement lies in the radius function, which is now larger than the one used in Nour and Takche (2025, Theorem 3.1).