\begin{tabbing}
case $x$ of 
\\[0ex]c\=onfig(${\it list}$) =$>$ ${\it config}$(${\it list}$)\+
\\[0ex]seq(${\it from}$,${\it to}$,${\it num}$) =$>$ ${\it seq}$(${\it from}$;${\it to}$;${\it num}$)
\-\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$case $x$ of inl($x$) =$>$ ${\it config}$($x$) $\mid$ inr($x$) =$>$ ${\it seq}$($x$.1;($x$.2).1;$x$.2.2)
\end{tabbing}