− v u 4 + 2 u 4 − 2 v 2 u 3 + 8 v u 3 − 6 u 3 + 7 v 2 u 2 − 13 v u 2 + 7 u 2 − 6 v 2 u + 8 v u − 2 u + 2 v 2 − v {\displaystyle -vu^{4}+2u^{4}-2v^{2}u^{3}+8vu^{3}-6u^{3}+7v^{2}u^{2}-13vu^{2}+7u^{2}-6v^{2}u+8vu-2u+2v^{2}-v}
