reserve X,Y,z,s for set, L,L1,L2,A,B for List of X, x for Element of X,
  O,O1,O2,O3 for Operation of X, a,b,y for Element of X, n,m for Nat;

theorem
  x.(O1 OR O2) = (x.O1)OR(x.O2) by RELSET_2:10;
