What is this fence made of?
The fence is made of metal.
    src        edge_attr  dst
0     0   to the left of   10
1     0  to the right of    8
2     0   to the left of   15
3     1   to the left of    7
4     1               on    2
5     3  to the right of   10
6     3  to the right of    6
7     3  to the right of   15
8     3  to the right of   12
9     5  to the right of   15
10    5  to the right of   12
11    6   to the left of    3
12    6  to the right of   10
13    6  to the right of   15
14    7  to the right of    1
15    7   to the left of   11
16    8   to the left of   12
17    8   to the left of   15
18    8   to the left of   16
19    8   to the left of    0
20    8   to the left of   10
21    9   to the left of   16
22    9   to the left of   12
23    9   to the left of   10
24   10  to the right of   16
25   10  to the right of    9
26   10   to the left of   14
27   10   to the left of    6
28   10  to the right of    8
29   10   to the left of    3
30   10  to the right of    0
31   11  to the right of    7
32   12  to the right of    9
33   12  to the right of    8
34   12   to the left of    3
35   12   to the left of    5
36   13               by    3
37   14  to the right of   16
38   14  to the right of   10
39   15   to the left of    6
40   15   to the left of    5
41   15  to the right of    8
42   15   to the left of    3
43   15  to the right of    0
44   16               of   12
45   16  to the right of    9
46   16  to the right of    8
47   16               on   12
48   16   to the left of   10
49   16   to the left of   14