What is the ladder on?
The ladder is on the fire truck.
    src        edge_attr  dst
0     0  to the right of    3
1     0             near    4
2     0  to the right of    9
3     0             near    6
4     1               of    0
5     1  to the right of    4
6     2   to the left of    7
7     3   to the left of    0
8     4   to the left of    1
9     4          next to    0
10    4             near    0
11    5   on the side of    0
12    5   to the left of    6
13    5               on    0
14    6             near    0
15    6  to the right of    5
16    6          next to    0
17    7  to the right of    2
18    9   to the left of    0
19   10   to the left of   13
20   12  on the front of    0
21   13  to the right of   10