Inverse Function

Definition: An inverse function of a function $f$ if a function $f^{-1}$ that reverses the mapping of $f$. If $f$ maps input $x$ to $y$, then $f^{-1}$ maps $y$ back to $x$.

Formally:

$$f^{-1}(y)=x⟺f(x)=y$$

Key Property: A function only has an inverse if it is Bijective.