− u 4 v 4 − u 4 v 3 − u 3 v 4 + 3 u 3 v 3 − 2 u 3 v 2 − 2 u 2 v 3 + 3 u 2 v 2 − 2 u 2 v − 2 u v 2 + 3 u v − u − v + 1 u 2 v 2 {\displaystyle -{\frac {u^{4}v^{4}-u^{4}v^{3}-u^{3}v^{4}+3u^{3}v^{3}-2u^{3}v^{2}-2u^{2}v^{3}+3u^{2}v^{2}-2u^{2}v-2uv^{2}+3uv-u-v+1}{u^{2}v^{2}}}}
