GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
# pmm (p2mm) # http://en.wikipedia.org/wiki/Wallpaper_group#Group_pmm M := [ [1,2], [1,4], [2,3], [3,6], [4,7], [6,9] ]; G1 := Group( (1,2) ); G2 := Group( (3,4) ); V := Group( (1,2), (3,4) ); iso := rec( 1 := V, 2 := G1, 3 := V, 4 := G2, 6 := G2, 7 := V, 9 := V ); mu := []; dim := 3; #matrix sizes pmm: # [ 8, 92, 512, 3022, 19904 ] #factors: # [ 11.5, 5.56522, 5.90234, 6.58637 ]