What is the shelf on?
The shelf is on the wall.
    src        edge_attr  dst
0     0   to the left of    3
1     0       sitting on    2
2     0   to the left of    4
3     3  to the right of    0
4     3   to the left of    7
5     4  to the right of    0
6     5   to the left of   11
7     5  to the right of   17
8     5   to the left of   13
9     5  to the right of    8
10    5  to the right of    6
11    6   to the left of   10
12    6   to the left of   18
13    6   to the left of   15
14    6  to the right of   14
15    6   to the left of    5
16    7  to the right of    3
17    8   to the left of   10
18    8   to the left of    5
19    8   to the left of   18
20    9   to the left of   11
21    9   to the left of   13
22    9               of    5
23    9               on    2
24   10  to the right of   17
25   10  to the right of    6
26   10  to the right of    8
27   11  to the right of    5
28   11  to the right of    9
29   13  to the right of    5
30   13  to the right of    9
31   14   to the left of   17
32   14   to the left of    6
33   14               on   10
34   15  to the right of   17
35   15  to the right of    6
36   17  to the right of   14
37   17   to the left of   18
38   17   to the left of    5
39   17   to the left of   15
40   17   to the left of   10
41   18  to the right of   17
42   18  to the right of    8
43   18  to the right of    6