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