از دستورات زیر استفاده کن
`
\begin{align*}
x\int_{0}^{x^{-1}}(1-\Re \phi(t))dt&=x\int_{0}^{x^{-1}}\int_{-\infty}^{\infty}(1-\cos(ty))F(dy)dt\\
&=x\int_{-\infty}^{\infty}\left[\int_{t=0}^{x^{-1}}(1-\cos(ty))dt\right]F(dy)\\
&=x\int_{-\infty}^{\infty}\left(x^{-1}-\frac{\sin (x^{-1}y)}{y}\right)F(dy)\\
&=\int_{-\infty}^{\infty}\left(1-\frac{\sin (x^{-1}y)}{x^{-1}y}\right)F(dy)
\end{align*}
`
