1gap> #constructing the same form over different fields 2gap> mat := 3> [[Z(2)^0,Z(2)^0,0*Z(2),0*Z(2)],[0*Z(2),Z(2)^0,0*Z(2),0*Z(2)], 4> [0*Z(2),0*Z(2),0*Z(2),Z(2)^0],[0*Z(2),0*Z(2),0*Z(2),0*Z(2)]]; 5[ [ Z(2)^0, Z(2)^0, 0*Z(2), 0*Z(2) ], [ 0*Z(2), Z(2)^0, 0*Z(2), 0*Z(2) ], 6 [ 0*Z(2), 0*Z(2), 0*Z(2), Z(2)^0 ], [ 0*Z(2), 0*Z(2), 0*Z(2), 0*Z(2) ] ] 7gap> form := QuadraticFormByMatrix(mat); 8< quadratic form > 9gap> WittIndex(form); 101 11gap> form := QuadraticFormByMatrix(mat,GF(4)); 12< quadratic form > 13gap> WittIndex(form); 142 15gap> quit; 16