\begin{definition}[Definition:Decimal Notation]
'''Decimal notation''' is the quotidian technique of expressing numbers in base $10$.
Every number $x \in \R$ is expressed in the form:
:$\ds x = \sum_{j \mathop \in \Z} r_j 10^j$
where:
:$\forall j \in \Z: r_j \in \set {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}$
\end{definition}