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 ^^ (B?) & A c= (B?) ^^ A
proof
  <%>E in B? by Th78;
  hence thesis by FLANG_1:16;
end;
