ABSTRACT
All spaces considered in this paper are assumed to be metric. Given a space X, we denote by BX(X,S} the (open) ball in X centered at a point x 6 X and having the radius e. For a subset A of X we define Nx(A, e) = (JaeA Bx(a,e) and we use the symbols Clx(A) and to denote the closure and the interior of A in X, respectively.
