es{-}prior{-}interface{-}vals(${\it es}$;$X$;$e$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$mapfilter($\lambda$$e$.$X$($e$);$\lambda$$e$.$e$ $\in_{b}$ $X$;es{-}before(${\it es}$; $e$))