def _registered_kl(type_a, type_b):
  """"""
  hierarchy_a = tf_inspect.getmro(type_a)
  hierarchy_b = tf_inspect.getmro(type_b)
  dist_to_children = None
  kl_fn = None
  for mro_to_a, parent_a in enumerate(hierarchy_a):
    for mro_to_b, parent_b in enumerate(hierarchy_b):
      candidate_dist = mro_to_a + mro_to_b
      candidate_kl_fn = _DIVERGENCES.get((parent_a, parent_b), None)
      if not kl_fn or (candidate_kl_fn and candidate_dist < dist_to_children):
        dist_to_children = candidate_dist
        kl_fn = candidate_kl_fn
  return kl_fn