\begin{definition}[Definition:Quintal Notation]
'''Quintal notation''' is the technique of expressing numbers in base $5$.
That is, every number $x \in \R$ is expressed in the form:
:$\ds x = \sum_{j \mathop \in \Z} r_j 5^j$
where:
:$\forall j \in \Z: r_j \in \set {0, 1, 2, 3, 4}$
\end{definition}