static <A> ItIt<L<A>> allSubsetsOfSize_iterator(int m, Cl<A> objects) {
  L<A> list = asList(objects);
  int n = l(list);
  ret mapI(allSpreads(n-m, m+1), spread -> {
    L<A> out = emptyList(m);
    int i = -1;
    for j to m: {
      i += spread.get(j)+1;
      out.add(list.get(i));
    }
    ret out;
  });
}