static IterableIterator<L<Int>> allSpreads(final int toSpread, final int buckets) {
  ret iff(new F0 {
    L<Int> collecting = ll(0);
    L<Int> remaining = ll(toSpread);

    public O get() {
      while true {
        ping();
        if (empty(collecting)) ret endMarker();
        
        // return list
        if (l(collecting) >= buckets-1) {
          L<Int> result = listPlus(collecting, last(remaining));
          dropLast(collecting);
          dropLast(remaining);
          setLast(collecting, last(collecting)+1);
          ret result;
        }
      
        // backtrace
        while (nempty(collecting) && last(collecting) >= last(remaining)) {
          dropLast(collecting);
          dropLast(remaining);
        }

        // done
        if (empty(collecting)) ret endMarker();
        
        // recurse
        collecting.add(0);
        remaining.add(last(remaining));
      }
    }
  });
}