Question: how to calculate the kernel of polynomial map in maple

r-x^4
u-(x^3)*y
v-x*y^3
w-y^4

Step 1
with(Groebner):
K := {r-x^4,u-(x^3)*y,v-x*y^3,w-y^4};
G := Basis(K, 'tord', degrevlex(r,u,v,w));

Step 2
G intersect k[r,u,v,w]

G2 := Basis({w*G[1],w*G[2],w*G[3],w*G[4],w*G[5],w*G[6],w*G[7],w*G[8],w*G[9],w*G[10],w*G[11],w*G[12],w*G[13],w*G[14], (1-w)*K[1], (1-w)*K[2], (1-w)*K[3], (1-w)*K[4]}, 'tord', degrevlex(r,u,v,w));

G2 has too much though include the correct solution

correct solution := {v*u-w*r,v^3-u*w^2,-u^2*w+v^2*r,u^3-v*r^2};
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