\begin{definition}[Definition:Rectangle Function]
The '''rectangle function''' is the real function $\Pi: \R \to \R$ defined as:
:$\forall x \in \R: \map \Pi x := \begin {cases} 1 : & \size x \le \dfrac 1 2 \\ 0 : & \size x > \dfrac 1 2 \end {cases}$
\end{definition}