\begin{definition}[Definition:Inverse Hyperbolic Secant/Complex/Definition 1]
The '''inverse hyperbolic secant''' is a multifunction defined as:
:$\forall z \in \C_{\ne 0}: \map {\sech^{-1} } z := \set {w \in \C: z = \map \sech w}$
where $\map \sech w$ is the hyperbolic secant function.
\end{definition}