%% gbdiff.sm1

[ (x,y) ring_of_differential_operators
  [[(Dx) 1 (Dy) 1]] weight_vector
 0
] define_ring

[ (x Dx + y Dy).
  (Dx^2 + Dy^2).
] /ff set

ff { [[(h). (1).]] replace homogenize} map /ff2 set

[ff2] groebner dehomogenize ::