\begin{diagram}{Set constructors}{setconstuctors}
\begin{mysyntdiag}
\synt{set\ constructor} \lit* [ 
\begin{stack}\\
 \begin{rep}[b] \synt{set\ group} \\ \lit* , \end{rep}
\end{stack}
\lit* ]
\end{mysyntdiag}
\begin{mysyntdiag}
\synt{set\ group} \synt{expression} 
\begin{stack}\\
\lit* {..} \synt{expression}
\end{stack}
\end{mysyntdiag}
\end{diagram}