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 |^ m) |^ n = (A |^ n) |^ m
proof
  thus (A |^ m) |^ n = A |^ (m * n) by FLANG_1:34
    .= (A |^ n) |^ m by FLANG_1:34;
end;
