What color do you think the rocks above the wall are?
The rocks are gray.
    src        edge_attr  dst
0     0   to the left of    9
1     0   to the left of    5
2     1  to the right of    3
3     2            above    6
4     3  to the right of    6
5     3   to the left of    1
6     3   to the left of    9
7     3               in    8
8     4   to the left of    9
9     5  to the right of    0
10    5   to the left of    9
11    6   to the left of    3
12    6            above   12
13    6  to the right of   13
14    7   to the left of    9
15    9  to the right of    0
16    9  to the right of    3
17    9  to the right of    4
18    9  to the right of    5
19    9  to the right of    7
20   13   to the left of    6