reserve x, x1, x2, y, z, X9 for set,
  X, Y for finite set,
  n, k, m for Nat,
  f for Function;
reserve F,Ch for Function;

theorem
  F is empty or union rng F is empty implies Intersection(F,Ch,y)=union
  rng F by RELAT_1:38,ZFMISC_1:2;
