ABSTRACT
Two measurable spaces (X, B ) and (Y, C) are called isomorphic iff there is a one-to-one function f from X onto Y such that f and f −1 are measurable. Two metric spaces (X, d) and (Y, e) will be called Borel-isomorphic, written X ~ Y, iff they are isomorphic with their σ-algebras of Borel sets.
