Inverse Hyperbolic Secant

$\begin{figure}\begin{center}\BoxedEPSF{ArcSech.epsf scaled 1000}\end{center}\end{figure}$

$\begin{figure}\begin{center}\BoxedEPSF{ArcSechReIm.epsf scaled 700}\end{center}\end{figure}$

The Inverse Function of the Hyperbolic Secant, denoted $\mathop{\rm sech}\nolimits ^{-1} x$ .