\[\sum_{m_{1}m_{2}}(2j_{3}+1)\begin{pmatrix}j_{1}&j_{2}&j_{3}\\
m_{1}&m_{2}&m_{3}\end{pmatrix}\begin{pmatrix}j_{1}&j_{2}&j^{\prime}_{3}\\
m_{1}&m_{2}&m^{\prime}_{3}\end{pmatrix}=\delta_{j_{3},j^{\prime}_{3}}\delta_{m%
_{3},m^{\prime}_{3}},\]