\[\frac{\sigma}{w-W}=\frac{z(z-1)W^{\prime}}{W(W-1)(W-z)}+\frac{\Theta_{0}}{W}+%
\frac{\Theta_{1}}{W-1}+\frac{\Theta_{2}-1}{W-z}=\frac{z(z-1)w^{\prime}}{w(w-1)%
(w-z)}+\frac{\theta_{0}}{w}+\frac{\theta_{1}}{w-1}+\frac{\theta_{2}-1}{w-z}.\]