 format  1  0
Bravais   = basis  (p2mm, 2-d space group)
2         = dim
3         = # symmetries

 1
    1.0  0.0    0.0
    0.0  1.0    0.0

 2 (2 0,0)
   -1.0	 0.0	0.0
    0.0 -1.0	0.0

 3 (m 0,y)
   -1.0	 0.0	0.0
    0.0	 1.0	0.0	
