$\forall$${\it es}$:ES, $A$:Type, $X$:AbsInterface($A$), $e$:E.
\\[0ex]es{-}prior{-}interface{-}vals(${\it es}$;$X$;$e$)
\\[0ex]=
\\[0ex]if $e$ $\in_{b}$ prior($X$)
\\[0ex]then es{-}prior{-}interface{-}vals(${\it es}$;$X$;prior($X$)($e$)) @ [$X$(prior($X$)($e$))]
\\[0ex]else []
\\[0ex]fi 
\\[0ex]$\in$ ($A$ List)