The Heaviside function is the D218: Boolean function \begin{equation} \mathbb{R} \to \{ 0, 1 \}, \quad x \mapsto \begin{cases} 1, \quad & x \geq 0 \\ 0, \quad & x < 0 \end{cases} \end{equation}

The Heaviside function is the D218: Boolean function \begin{equation} \mathbb{R} \to \{ 0, 1 \}, \quad x \mapsto I_{[0, \infty)}(x) \end{equation}