What is the fence post before?
The fence post is in front of the fence.
    src        edge_attr  dst
0     0      in front of    5
1     0  to the right of    9
2     0  to the right of    6
3     1   to the left of   18
4     1   to the left of    8
5     1   to the left of   12
6     1   to the left of    7
7     1  to the right of    6
8     2      taller than    5
9     2      taller than   17
10    2      in front of    5
11    3   to the left of    9
12    4   to the left of    9
13    5      in front of   13
14    5           behind    0
15    5           behind    2
16    6      in front of   13
17    6   to the left of    0
18    6   to the left of    1
19    6   to the left of   14
20    7  to the right of    1
21    7  to the right of   14
22    8  to the right of   14
23    8  to the right of    1
24    9   to the left of    0
25    9  to the right of    3
26    9  to the right of    4
27   12  to the right of   14
28   12  to the right of    1
29   13           behind    5
30   13           behind    6
31   13           behind   15
32   14   to the left of    7
33   14   to the left of    8
34   14   to the left of   12
35   14   to the left of   18
36   14  to the right of    6
37   15      in front of   13
38   18  to the right of    1
39   18  to the right of   14