LIB "modules.lib";
"Example:"; 
==> Example:
ring R = 0,(x,y,z),dp;
matrix a[2][3] = -x,-y^2,x^3,y,x,0;
matrix b[1][2] = x^2-y^3,xy;
Matrix A = a;
Matrix B = b;
Module M = coker(A);
Module N = coker(B);
hom(M,N);
==> subquotient (| 0  -y -y 0  -x  |, | -y3+x2 xy 0      0  |)
==>              | xy -x -x y3 -y2 |  | 0      0  -y3+x2 xy | 
==> 
==>