Farthest Points and Subdifferential in 𝑝-Normed Spaces

Abstract

We study the farthest point mapping in a 𝑝-normed space 𝑋 in virtue of subdifferential of 𝑟(𝑥)=sup{‖𝑥−𝑧‖𝑝∶𝑧∈𝑀}, where 𝑀 is a weakly sequentially compact subset of 𝑋. We show that the set of all points in 𝑋 which have farthest point in 𝑀 contains a dense 𝐺𝛿 subset of 𝑋.