The absolute value function is the D4367: Unsigned real function
\begin{equation}
\mathbb{R} \to [0, \infty), \quad
x \mapsto
\begin{cases}
x, \quad & x \geq 0 \\
-x, \quad & x < 0
\end{cases}
\end{equation}
The absolute value function is the D4367: Unsigned real function
\begin{equation}
\mathbb{R} \to [0, \infty), \quad
x \mapsto x I_{[0, \infty)}(x) - x I_{(- \infty, 0)}(x)
\end{equation}
