gap> M:=ClosedSurface(2);;
gap> N:=SimplicialK3Surface();;
gap> W:=WedgeSum(M,N);;
gap> A:=CohomologyRing(W,2);
&lt;algebra of dimension 29 over GF(2)&gt;
gap> x:=Basis(A)[25];
v.25
gap> y:=Basis(A)[27];
v.27
gap> x*y;
v.29
