What is in front of the sky?
The clock tower is in front of the sky.
   src        edge_attr  dst
0    0      in front of    3
1    1  to the right of    4
2    3           behind    0
3    3   to the left of    4
4    4   on the side of    0
5    4   to the left of    1
6    4  to the right of    3