A D63: Finite sequence $(x_0, x_1, x_2, x_3, x_4, x_5, x_6, x_7)$ is a byte if and only if \begin{equation} x_0, x_1, x_2, x_3, x_4, x_5, x_6, x_7 \in \{ 0, 1 \} \end{equation}