\begin{definition}[Definition:Involution (Mapping)/Definition 3]
Let $A$ be a set.
Let $f: A \to A$ be a mapping on $A$.
$f$ is an involution {{iff}} $f$ is both a bijection and a symmetric relation.
That is, {{iff}} $f$ is a bijection such that:
:$f = f^{-1}$
\end{definition}