list\_accum($x$,$a$.$f$($x$;$a$); $y$; $l$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$rec{-}case($l$) of [] =$>$ $y$ $\mid$ $b$::${\it l'}$ =$>$ .list\_accum($x$,$a$.$f$($x$;$a$); $f$($y$;$b$); ${\it l'}$)
\\[0ex]\emph{(recursive)}