Formula_20001

\[f(p, q)=\sum_{f_{m_{1}, \ldots, m_{N}, m_{1}^{\prime}, \ldots, m_{N}^{\prime}}} p_{1}^{m_{1}} \ldots p_{N}^{m_{N}} q_{1}^{m_{1}^{\prime}} \ldots q_{N}^{m_{N}^{\prime}}\]