static <A> LL<A> chunksOf1000(Collection<A> c) {
  new LL<A> out;
  Iterator<A> it = iterator(c);
  L<A> l = new L(1000);
  while (it.hasNext()) {
    l.add(it.next());
    if (l(l) >= 1000) {
      out.add(l);
      l = new L(1000);
    }
  }
  if (nempty(l)) out.add(l);
  ret out;
}