GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
#3 6x6 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 -1 1 1 0 0 0 0 -1 1 6x6 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 -1 -1 0 0 0 1 0 0 1 0 0 -1 0 0 1 0 0 0 -1 1 0 6x6 1 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 1 -1 0 1 1 0 0 -1 0 -1 1 0 0 0 0 0 0 1 -1 0 dim6/2-1,2-1;2-1a