\begin{tabbing}
combine{-}halt{-}info(${\it ea}$;${\it eb}$;$f$;$g$;$x$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if isl($x$)$\rightarrow$ $x$\+
\\[0ex]else priority{-}select(\=$\lambda$$m$.deq{-}member(NatDeq;$m$;0.${\it ea}$) $\wedge_{2}$ $f$($m$);\+
\\[0ex]$\lambda$$m$.deq{-}member(NatDeq;$m$;0.${\it eb}$) $\wedge_{2}$ $g$($m$);0.merge(${\it ea}$;${\it eb}$)) fi
\-\-
\end{tabbing}