static <A> IterableIterator<L<A>> allCombinations(final LL<A> base) {
  ret iteratorFromFunction(new F0<L<A>>() {
    final int n = l(base);
    L<Int> l = rep((Int) 0, n);
    
    public L<A> get() {
      if (l == null) null;
      L<A> out = makeList();
      int i = 0;
      while (i < n) {
        int n = l.get(i);
        if (n+1 < l(base.get(i))) {
          l.set(i, n+1);
          break;
        }
        l.set(i++, 0);
      }
      if (i >= n) l = null;
      ret out;
    }
    
    L<A> makeList() {
      L<A> list = emptyList(n);
      for i to n:
        list.add(base.get(i).get(l.get(i)));
      ret list;
    }
  });
}