reserve x for set;
reserve a, b, c, d, e for Real;
reserve m, n, m1, m2 for Nat;
reserve k, l for Integer;
reserve p for Rational;

theorem
  2 to_power 4 = 16
proof
  thus 2 to_power 4 = 2 to_power (2+2) .= (2 to_power 2)*(2 to_power 2) by Th27
    .= 16 by Th60;
end;
