Is the wall behind the shelf?
Yes, the wall is behind the shelf.
    src        edge_attr  dst
0     0  to the right of   11
1     0  to the right of    1
2     0  to the right of   16
3     1           behind   16
4     1   to the left of    0
5     1   to the left of   11
6     2   to the left of    6
7     4               on   10
8     4      in front of   12
9     4   to the left of    6
10    4            above   10
11    5   to the left of    6
12    6               on   10
13    6  to the right of    2
14    6  to the right of    5
15    6  to the right of    4
16    6  to the right of   13
17    6  to the right of   12
18    6  to the right of   15
19    7   to the left of   16
20    8               in    9
21    8               on   16
22    9   to the left of   14
23   10            under    4
24   11   to the left of    0
25   11  to the right of    1
26   12           behind    4
27   12   to the left of    6
28   13   to the left of    6
29   13               on   12
30   14               on   16
31   14  to the right of    9
32   15               by    4
33   15               on   10
34   15   to the left of    6
35   16   to the left of    0
36   16  to the right of    7
37   16               on    1
38   16      in front of    1