theorem
  for X, Y being complex-membered set
  holds multRel(X,z) \/ multRel(Y,z) c= multRel(X \/ Y,z)
proof
  let X, Y be complex-membered set;
  X c= X \/ Y & Y c= X \/ Y by XBOOLE_1:7;
  then multRel(X,z) c= multRel(X \/ Y,z) & multRel(Y,z) c= multRel(X \/ Y,z)
    by Th47;
  hence thesis by XBOOLE_1:8;
end;
