The cars are on what?
The cars are on the shelf.
    src        edge_attr  dst
0     0  to the right of    9
1     0  to the right of    2
2     1   to the left of   20
3     1  to the right of   15
4     2   to the left of    0
5     3  to the right of   17
6     4               on   15
7     4   to the left of    9
8     5  to the right of   17
9     6  to the right of   11
10    6   to the left of   20
11    6  to the right of   13
12    6   to the left of   21
13    8     hanging from    7
14    9   to the left of    0
15    9  to the right of    4
16    9  to the right of   15
17    9  to the right of   16
18   10  to the right of   16
19   11   to the left of   20
20   11  to the right of   16
21   11   to the left of    6
22   12        on top of   13
23   13  to the right of   17
24   13   to the left of   20
25   13   to the left of    6
26   13  to the right of   16
27   13   to the left of   21
28   15   to the left of    9
29   15   to the left of    1
30   16        on top of   15
31   16   to the left of    9
32   16   to the left of   10
33   16   to the left of   11
34   16   to the left of   13
35   17   to the left of    5
36   17   to the left of    3
37   17   to the left of   13
38   20  to the right of    6
39   20  to the right of   11
40   20  to the right of   13
41   20  to the right of    1
42   21        on top of   20
43   21  to the right of    6
44   21  to the right of   13