\[\int w^{\prime}_{1}w^{\prime}_{2}\,\mathrm{d}z=\tfrac{1}{3}(w_{1}w^{\prime}_{2%
}+w^{\prime}_{1}w_{2}+zw^{\prime}_{1}w^{\prime}_{2}-z^{2}w_{1}w_{2}),\]