Proof of Lemma 1. (1) The 'if' part is obvious. For the 'only if' part, note that for any given v,Therefore, if CCD(U, V ) = 0, then we must have Var[F V |U (v|U )] = 0, for nearly all v. In other words, random variableand this observation holds true for nearly all v. Thus V and U must be independent.(2) The 'if' part again is obvious. For the 'only if' part, note that CCD(U, V ) =for nearly all u and v. In other words, thatmeasurable, so is I V (v) and hence a function of U . Since such observation holds true for all v, it could be concluded that V is a function of U . The same line of arguments could be applied to C U |V (u) = 0, to deduce that U is also a function of V . This completes the proof.