adj(M: MAT): MAT

/**/  Use R ::= QQ[t,x,y,z];
/**/  adj(mat([[x,y,z],[t,y,x],[x,x^2,x*y]]));
matrix( /*RingWithID(44, "QQ[t,x,y,z]")*/
 [[-x^3 +x*y^2, -x*y^2 +x^2*z, x*y -y*z],
  [-t*x*y +x^2, x^2*y -x*z, -x^2 +t*z],
  [t*x^2 -x*y, -x^3 +x*y, -t*y +x*y]])

/**/   Z5 := NewRingFp(5);
/**/   adj(matrix(Z5, [[1,2],[3,1]]));
matrix( /*FFp(5)*/
 [[1, -2],
  [2, 1]])