\begin{tabbing}
prior{-}$f${-}fixedpoints($e$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if $f$($e$) = $e$\+
\\[0ex]then if $e$ $\in_{b}$ prior(${\it Sys}$) then prior{-}$f${-}fixedpoints(prior(${\it Sys}$)($e$)) @ [$e$] else [$e$] fi 
\\[0ex]else prior{-}$f${-}fixedpoints($f$$\ast\ast$($e$))
\\[0ex]fi 
\\[0ex]
\-\\[0ex]{\em clarification:}
\\[0ex]
\\[0ex]es{-}prior{-}fixedpoints\=\{i:l\}\+
\\[0ex](${\it es}$; ${\it Sys}$; $f$; $e$)
\-\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if es{-}eq{-}E(${\it es}$; ($f$($e$)); $e$)\+
\\[0ex]then \=if $e$ $\in_{b}$ es{-}prior{-}interface\{i:l\}(${\it es}$; ${\it Sys}$)\+
\\[0ex]then \=es{-}prior{-}fixedpoints\=\{i:l\}\+\+
\\[0ex](${\it es}$; ${\it Sys}$; $f$; es{-}prior{-}interface\{i:l\}(${\it es}$; ${\it Sys}$)($e$))
\-\\[0ex]@ [$e$ / []]
\-\\[0ex]else [$e$ / []]
\\[0ex]fi 
\-\\[0ex]else es{-}prior{-}fixedpoints\=\{i:l\}\+
\\[0ex](${\it es}$; ${\it Sys}$; $f$; es{-}fix(${\it es}$;$f$;$e$))
\-\\[0ex]fi 
\-\\[0ex]\emph{(recursive)}
\end{tabbing}