Is the shelf made of glass?
Yes, the shelf is made of glass.
    src        edge_attr  dst
0     0   to the left of   17
1     0   to the left of   11
2     0   to the left of    4
3     0   to the left of   20
4     0   to the left of   13
5     2  to the right of    4
6     3   to the left of   16
7     3  to the right of   13
8     4  to the right of   17
9     4   to the left of   18
10    4  to the right of    0
11    4   to the left of    2
12    4   to the left of    6
13    4  to the right of    7
14    4   to the left of   10
15    5   to the left of    6
16    6  to the right of    4
17    6  to the right of   17
18    6   to the left of   18
19    6  to the right of    5
20    7   to the left of   20
21    7   to the left of    4
22    7   to the left of   13
23    7   to the left of   17
24    7   to the left of   11
25   10               in   11
26   10   to the left of   18
27   10  to the right of   17
28   10  to the right of   13
29   10  to the right of    4
30   11  to the right of    0
31   11   to the left of   18
32   11  to the right of    7
33   13  to the right of    7
34   13   to the left of   10
35   13   to the left of   15
36   13   to the left of    3
37   13   to the left of   21
38   13   to the left of   16
39   13   to the left of   19
40   13  to the right of    0
41   15  to the right of   13
42   16  to the right of   13
43   16  to the right of    3
44   17   to the left of    6
45   17  to the right of    7
46   17  to the right of    0
47   17   to the left of    4
48   17   to the left of   10
49   18  to the right of   11
50   18  to the right of   10
51   18  to the right of    6
52   18  to the right of    4
53   19  to the right of   13
54   19               in   11
55   20  to the right of    0
56   20  to the right of    7
57   21  to the right of   13