− v 2 u 4 + 2 v u 4 − u 4 + 4 v 2 u 3 − 8 v u 3 + 4 u 3 − 6 v 2 u 2 + 13 v u 2 − 6 u 2 + 4 v 2 u − 8 v u + 4 u − v 2 + 2 v − 1 {\displaystyle -v^{2}u^{4}+2vu^{4}-u^{4}+4v^{2}u^{3}-8vu^{3}+4u^{3}-6v^{2}u^{2}+13vu^{2}-6u^{2}+4v^{2}u-8vu+4u-v^{2}+2v-1}
