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