public static <A> List<List<A>> product(List<A> l) {
        if (l.isEmpty())
            return Collections.singletonList(Collections.emptyList());
        A hd = l.get(0);
        List<List<A>> res = new ArrayList<>();
        List<List<A>> rec = product(l.subList(1, l.size()));
        // Combinations with hd
        for (List<A> r : rec) {
            List<A> hd_r = new ArrayList<>();
            hd_r.add(hd);
            hd_r.addAll(r);
            res.add(hd_r);
        }
        // Combinations without hd
        res.addAll(rec);
        return res;
    }

    public static void main(String[] args) {
        List<Integer> set = new ArrayList<>();
        set.add(0);
        set.add(1);
        set.add(2);
        set.add(3);
        List<List<Integer>> product = product(set);
        System.out.println(product);
    }