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:
 * $\sec^{-1} \left({x}\right) := \left\{{y \in \R: \sec \left({y}\right) = x}\right\}$

where $\sec \left({y}\right)$ is the secant of $y$.