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