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