K993 :

a b^5 c^6 x^2 y-b^4 c^8 x^2 y-a^5 b c^6 x y^2+a^4 c^8 x y^2+b^8 c^4 x^2 z-a b^6 c^5 x^2 z-a^8 c^4 y^2 z+a^6 b c^5 y^2 z-a^4 b^8 x z^2+a^5 b^6 c x z^2+a^8 b^4 y z^2-a^6 b^5 c y z^2=0