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= A?
proof
  A? = {<%>E} \/ A by Th76;
  hence thesis by XBOOLE_1:7;
end;
