Is the sky clear?
Yes, the sky is clear.
    src        edge_attr  dst
0     1   to the left of   10
1     1   to the left of    6
2     2               on    4
3     2   to the left of    3
4     2  to the right of   12
5     3  to the right of    2
6     3  to the right of    4
7     4   to the left of    3
8     6  to the right of    1
9     6  to the right of    9
10    6      in front of   13
11    9   to the left of    6
12    9   to the left of   10
13   10  to the right of    1
14   10  to the right of    9
15   12   to the left of    2