gap> qL:=IntersectionForm(L);;
gap> qM:=IntersectionForm(M);;
gap> qN:=IntersectionForm(N);;
gap> Display(qL);
[ [  -2,   1 ],
  [   1,   0 ] ]
gap> Display(qM);
[ [  1,  0 ],
  [  0,  1 ] ]
gap> Display(qN);
[ [   1,   0 ],
  [   0,  -1 ] ]
