Main result: For each closed convex subset C of a Banach space X and each x is not an element of C there exists an equivalent norm on X for which x has a unique nearest point in C.
机构:
Univ Catania, Dipartimento Matemat & Informat, Viale A Doria 6, I-95125 Catania, ItalyUniv Catania, Dipartimento Matemat & Informat, Viale A Doria 6, I-95125 Catania, Italy