reserve E, x, y, X for set;
reserve A, B, C for Subset of E^omega;
reserve a, b for Element of E^omega;
reserve i, k, l, kl, m, n, mn for Nat;

theorem
  A c= C? & B c= C? implies A ^^ B c= C |^ (0, 2)
proof
  assume A c= C? & B c= C?;
  then A ^^ B c= (C?) ^^ (C?) by FLANG_1:17;
  hence thesis by Th93;
end;
