Definition:Inverse Tangent/Real

Definition
Let $x \in \R$ be a real number.

The inverse tangent of $x$ is the multifunction defined as:
 * $\tan^{-1} \left({x}\right) := \left\{{y \in \R: \tan \left({y}\right) = x}\right\}$

where $\tan \left({y}\right)$ is the tangent of $y$.