def _log_ndtr_lower(x, series_order):
  """"""
  x_2 = tf.square(x)
  # Log of the term multiplying (1 + sum)
  log_scale = -0.5 * x_2 - tf.math.log(-x) - 0.5 * np.log(2. * np.pi)
  return log_scale + tf.math.log(_log_ndtr_asymptotic_series(x, series_order))