static Map<S, S> getSnippetTitles_cached(Collection<S> ids) ctex {
  new L<S> remaining;
  new HashMap<S, S> map;
  for (S id : ids) {
    S title = getSnippetTitle_cached_probe(id);
    if (title != null)
      map.put(fsI(id), title);
    else
      remaining.add(id);
  }
  SS map2 = getSnippetTitles(remaining);
  for (S id : keys(map2))
    getSnippetTitle_cached_put(id, map2.get(id));
  map.putAll(map2);
  ret map;
}