Nerve is of dimension 1 - 41 simplices - 21 vertices.
Iterator on Nerve simplices
0 
1 
2 
2 0 
3 
3 1 
4 
4 3 
5 
5 2 
6 
6 4 
7 
7 5 
8 
9 
9 6 
10 
10 7 
11 
12 
12 8 
13 
13 9 
13 10 
14 
14 11 
15 
15 13 
16 
16 12 
17 
17 14 
18 
18 15 
18 16 
18 17 
19 
19 18 
20 
20 19