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Multiplying a bit by $2$ we always obtain $0$.  \end{quote}  There exist particular phenomena such the one related with time that have a kind of {\em ciclicity}. We focus on two examples  \begin{enumerate}  \item The day of the week, or if you like music the musical notes, that are $7$;  \item The hour of a day that we assume are $12$, as in a analogic clock.  \end{enumerate}  The $2$ examples are similar in some sense. In fact we have that the first day of a week is Monday, the $8^{th}$ is Monday again, the same happens for the musical notes. The first hour is $1$, and the $13^{th}$ hour is $1$ again.