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 Th60:
  2 to_power 2 = 4
proof
  thus 2 to_power 2 = 2^2 by Th46
    .= 4;
end;
