docs: def _normalize_abmn(abmn):
      """return a normalized version of abmn
      """
      abmn_2d = np.atleast_2d(abmn)
      abmn_normalized = np.hstack((
          np.sort(abmn_2d[:, 0:2], axis=1),
          np.sort(abmn_2d[:, 2:4], axis=1),
      ))
      return abmn_normalized