9(0)->$->7
9(0)->$->10
7(0)->$->1
7(0)->$->5
1(0)->a->2
2(0)->$->3
3(0)->a->4
4(0)->$->8
8(0)->$->7
8(0)->$->10
10(0)->$->11
11(0)->a->12
12(0)->$->21
21(0)->$->19
21(0)->$->22
19(0)->$->13
19(0)->$->15
13(0)->a->14
14(0)->$->20
20(0)->$->19
20(0)->$->22
22(1)
15(0)->b->16
16(0)->$->17
17(0)->b->18
18(0)->$->20
5(0)->b->6
6(0)->$->8