digraph G {
            5 -> 6;
            6 -> 3;
            6 -> 7;
            7 -> 2;
            7 -> 4;
            8 -> 6;
            9 -> 8;
            10 -> 9;
            11 -> 10;
            12 -> 5;
            12 -> 6;
            13 -> 0;
            13 -> 1;
            13 -> 21;
            14 -> 6;
            15 -> 13;
            15 -> 14;
            16 -> 17;
            16 -> 19;
            16 -> 20;
            17 -> 11;
            17 -> 12;
            19 -> 15;
            19 -> 18;
            20 -> 18;
        }