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