余弦積分の極限
\[\lim_{x\rightarrow\pm0}\left\{ \Ci\left(\alpha x\right)-\Ci\left(x\right)\right\} =\begin{cases}\Log\alpha & x\rightarrow+0\\\Log\left(-\alpha\right)-\pi i & x\rightarrow-0\end{cases}\]
指数積分・正弦積分・余弦積分の定義
\[\Si\left(x\right):=\int_{0}^{x}\frac{\sin x}{x}dx\]