w{-}isrcvl($w$; $l$; $a$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$($\neg_{b}$w{-}isnull($w$; $a$)) $\wedge_{b}$ isrcv(w{-}kind($w$; $a$)) $\wedge_{b}$ lnk(w{-}kind($w$; $a$)) = $l$