Definition:Inverse Secant/Real

Definition
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 $y$.