\[(z\sigma^{\prime\prime}-\sigma^{\prime})^{2}+2\left((\sigma^{\prime})^{2}-%
\kappa_{0}^{2}\kappa_{\infty}^{2}z^{2}\right)(z\sigma^{\prime}-2\sigma)+8%
\kappa_{0}\kappa_{\infty}\theta_{0}\theta_{\infty}z\sigma^{\prime}=4\kappa_{0}%
^{2}\kappa_{\infty}^{2}(\theta_{0}^{2}+\theta_{\infty}^{2})z^{2}.\]