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 Th12:
  (A |^ m) ^^ (A |^ n) = (A |^ n) ^^ (A |^ m)
proof
  thus (A |^ m) ^^ (A |^ n) = A |^ (m + n) by FLANG_1:33
    .= (A |^ n) ^^ (A |^ m) by FLANG_1:33;
end;
