What are the items of furniture that the books are sitting on?
The pieces of furniture are shelves.
    src        edge_attr  dst
0     0       hanging on    9
1     0   to the left of   17
2     0   to the left of   18
3     0   to the left of   13
4     0   to the left of    8
..  ...              ...  ...
69   18   to the left of   13
70   18  to the right of   12
71   18   to the left of    3
72   18  to the right of    9
73   18  to the right of    8

[74 rows x 3 columns]