\begin{center}
\begin{tabular}{|c|c|c|} \hline
Category          & Intuitive meaning & Typical
                                        element  \\ \hline
                                                    \hline
$\mathit{Nml}$    & numerals          & $N$      \\ \hline
$\mathit{UnOps}$  & unary operators   & $\alpha$ \\ \hline
$\mathit{BinOps}$ & binary operators  & $\omega$ \\ \hline
$\mathit{Ide}$    & identifiers       & $I$      \\ \hline
$\mathit{Exp}$    & expressions       & $E$      \\ \hline
$\mathit{Cmd}$    & commands          & $C$      \\ \hline
\end{tabular}
\end{center}


