static <A> TreeSet<A> concatListsToTreeSet(Collection<? extends Cl<A>> lists) {
  new TreeSet<A> l;
  for (Cl<A> list : lists)
    if (list != null)
      l.addAll(list);
  ret l;
}

static <A> TreeSet<A> concatListsToTreeSet(Cl<A>... lists) {
  ret concatListsToTreeSet(asList(lists));
}