Ternary spaces, media, and Chebyshev sets

Closed Sets and Generators in Ternary Hamming Spaces 1

The n-dimensional ternary Hamming space is Tn, where T = f0; 1; 2g. Three points in Tn form a line if they have in common excactly n 1 components. A subset of Tn is closed if, whenever it contains two points of a line, it contains also the third one. A generator is a set, whose closure is Tn. In this paper, we investigate several properties of closed sets and generators. Two alternative proofs ...

Proximality and Chebyshev sets

This paper is a companion to a lecture given at the Prague Spring School in Analysis in April 2006. It highlights four distinct variational methods of proving that a finite dimensional Chebyshev set is convex and hopes to inspire renewed work on the open question of whether every Chebyshev set in Hilbert space is convex.

ε-weakly Chebyshev subspaces and quotient spaces

Bregman distances and Chebyshev sets

A closed set of a Euclidean space is said to be Chebyshev if every point in the space has one and only one closest point in the set. Although the situation is not settled in infinite-dimensional Hilbert spaces, in 1932 Bunt showed that in Euclidean spaces a closed set is Chebyshev if and only if the set is convex. In this paper, from the more general perspective of Bregman distances, we show th...

Well Posed Optimization Problems and Nonconvex Chebyshev Sets in Hilbert Spaces

A result on the existence and uniqueness of metric projection for certain sets is proved, by means of a saddle point theorem. A conjecture, based on such a result and aiming for the construction of a nonconvex Chebyshev set in a Hilbert space, is presented.