What do the locomotive and the car have in common?
The color, both the locomotive and the car are red.
    src        edge_attr  dst
0     0  to the right of   10
1     0  to the right of    8
2     0  to the right of   11
3     1  to the right of    6
4     2  to the right of    6
5     2  to the right of    9
6     4   to the left of   11
7     4   to the left of   10
8     4   to the left of    5
9     5  to the right of   14
10    5  to the right of    4
11    5            below    7
12    6   to the left of    2
13    6   to the left of    1
14    7            above    5
15    8   to the left of    0
16    9   to the left of    2
17   10   to the left of    0
18   10  to the right of    4
19   11   to the left of    0
20   11  to the right of    4
21   14   to the left of    5