static <A, B> LL<B> multiValuesAsListOfLists(MultiMap<A, B> mm) {
  if (mm == null) null;
  new LL<B> out;
  for (A key : mm.keySet())
    if (l(mm.get(key)) > 1)
      out.add(cloneList(mm.get(key)));
  ret out;
}