On which side is the trailer?
The trailer is on the left of the image.
    src        edge_attr  dst
0     1   to the left of   16
1     1  to the right of    2
2     1  to the right of    8
3     1  to the right of    3
4     2   to the left of    1
5     2  to the right of    3
6     2   to the left of   16
7     2  to the right of    9
8     2  to the right of    8
9     3   to the left of   21
10    3   to the left of    1
11    3  to the right of    9
12    3   to the left of    2
13    4   to the left of    7
14    4  to the right of   18
15    6               in    5
16    6  to the right of   15
17    7  to the right of    4
18    7  to the right of   18
19    8   to the left of   16
20    8   to the left of   21
21    8        pulled by   21
22    8   to the left of    1
23    8   to the left of    2
24    9   to the left of   13
25    9   to the left of   21
26    9   to the left of    3
27    9   to the left of    2
28   10  to the right of   21
29   11   to the left of   17
30   13   to the left of   21
31   13  to the right of    9
32   14  to the right of   21
33   15   to the left of    6
34   15   to the left of   20
35   16  to the right of    1
36   16  to the right of    8
37   16  to the right of    2
38   17   to the left of   20
39   17  to the right of   11
40   18   to the left of    4
41   18   to the left of    7
42   19  to the right of   21
43   20  to the right of   15
44   20  to the right of   17
45   21          pulling    8
46   21  to the right of    3
47   21  to the right of   13
48   21   to the left of   10
49   21   to the left of   14
50   21  to the right of    8
51   21   to the left of   19
52   21  to the right of    9