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 Th79:
  A? = A |^ (0, 1)
proof
  thus A? = (A |^ 0) \/ (A |^ (0 + 1)) by Th75
    .= A |^ (0, 1) by Th28;
end;
