Does this train look black?
Yes, the train is black.
    src        edge_attr  dst
0     0   to the left of    1
1     1  to the right of    0
2     3  to the right of    9
3     4  to the right of    9
4     5   to the left of   10
5     5  to the right of   14
6     6  to the right of    7
7     7  to the right of   10
8     7   to the left of    6
9     8  to the right of    9
10    9   to the left of    4
11    9   to the left of    3
12    9   to the left of    8
13    9  to the right of   14
14   10   to the left of    7
15   10  to the right of    5
16   10  to the right of   14
17   14   to the left of    5
18   14   to the left of    9
19   14   to the left of   10