差分

$$\begin{align*}

=&\frac{1}{s}\sum_{k=0}^{s-1}\left[\left(e^{\frac{m}{s}\cdot2\pi i}\right)^ke^{\left(e^{\frac{2\pi i}{s}}\right)^kx}\right]\\

=&\frac{1}{s}\sum_{k=0}^{s-1}\left[\exp\left(\frac{2km\pi}{s}i+\exp\left(\frac{2k\pi}{s}i\right)x\right)\right]