What's the snow covering?
The snow is covering the rocks.
    src        edge_attr  dst
0     0   to the left of   10
1     0   to the left of    7
2     0   to the left of   11
3     2         covering    3
4     3  to the right of    4
5     3  to the right of    8
6     3       covered by    2
7     3   to the left of   12
8     4   to the left of    3
9     7  to the right of    0
10    7   to the left of   10
11    8   to the left of    3
12    9          holding    0
13    9   to the left of   10
14   10  to the right of    0
15   10  to the right of    9
16   10  to the right of    7
17   11  to the right of    0
18   12  to the right of    3