gap> B:=[ [ 0, 1, -1, -1, 1, 0 ],
> [ 1, 0, 1, 1, 0, 0 ],
> [ 0, 0, 1, 0, 0, 0 ],
> [ 0, 0, 0, 1, -1, 0 ],
> [ 0, 0, 1, 1, 0, 0 ],
> [ 0, 0, 1, 1, 0, 1 ] ];;
gap> Display(IntersectionForm(M,B));
[ [ 0, 1, 0, 0, 0, 0 ],
[ -1, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 1, 0 ],
[ 0, 0, 0, 0, 0, 1 ],
[ 0, 0, -1, 0, 0, 0 ],
[ 0, 0, 0, -1, 0, 0 ] ]