− v 2 u 4 + 2 v u 4 − u 4 + 4 v 2 u 3 − 8 v u 3 + 5 u 3 − 7 v 2 u 2 + 13 v u 2 − 7 u 2 + 5 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}+5u^{3}-7v^{2}u^{2}+13vu^{2}-7u^{2}+5v^{2}u-8vu+4u-v^{2}+2v-1}
