\begin{definition}[Definition:Inverse Secant/Real]
Let $x \in \R$ be a real number such that $x \le -1$ or $x \ge 1$.
The '''inverse secant of $x$''' is the multifunction defined as:
:$\map {\sec^{-1} } x := \set {y \in \R: \map \sec y = x}$
where $\map \sec y$ is the secant of $y$.
\end{definition}