***** a2,1 *****

3 cosets
2 double cosets
Sizes:
0: ()
      [1]	1
1: (1)
      [2]	q + q^2

Neighbours of a point in 0:
1:  [2]		q + q^2

Neighbours of a point in 1:
0:  [1]		1
1:  [1]		-1 + q + q^2