public static void main(String[] args) {
        ArrayList<Integer> S = new ArrayList<Integer>();
        if (args.length >= 1) {
            for (int i = 0; i < args.length; ++i) {
                S.add(Integer.parseInt(args[i]));
            }
        } else {
            Random r = new Random();
            int count = r.nextInt(10) + 1;
            for (int i = 0; i < count; ++i) {
                S.add(i);
            }
        }
        generate_power_set(S);
    }