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