\begin{definition}[Definition:Reciprocal]
Let $x \in \R$ be a real number such that $x \ne 0$.
Then $\dfrac 1 x$ is called the '''reciprocal of $x$'''.
The real function $f: \R_{\ne 0} \to \R$ defined as:
:$\forall x \in \R_{\ne 0}: \map f x = \dfrac 1 x$ 
is called the '''reciprocal function'''.
\end{definition}