\begin{tabbing}
combine{-}halt{-}info(${\it ea}$; ${\it eb}$; $f$; $g$; $x$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if isl($x$)\+
\\[0ex]then $x$
\\[0ex]else priority{-}select(\=($\lambda$$m$.band(deq{-}member(nat{-}deq; $m$; cons(0; ${\it ea}$)); ($f$($m$))));\+
\\[0ex]($\lambda$$m$.band(deq{-}member(nat{-}deq; $m$; cons(0; ${\it eb}$)); ($g$($m$))));
\\[0ex]cons(0; merge(${\it ea}$; ${\it eb}$)))
\-\\[0ex]fi 
\-
\end{tabbing}