\[\frac{{\mathrm{d}}^{2}}{{\mathrm{d}z}^{2}}\operatorname{sc}\left(z,k\right)=(1%
+{k^{\prime}}^{2})\operatorname{sc}\left(z,k\right)+2{k^{\prime}}^{2}{%
\operatorname{sc}}^{3}\left(z,k\right),\]