\[\int zw_{1}w_{2}\,\mathrm{d}z=\tfrac{1}{6}(w_{1}w^{\prime}_{2}+w^{\prime}_{1}w%
_{2})-\tfrac{1}{3}(zw^{\prime}_{1}w^{\prime}_{2}-z^{2}w_{1}w_{2}),\]