w{-}isrcvl($w$; $l$; $a$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\neg_{2}$w{-}isnull($w$; $a$) $\wedge_{2}$ isrcv(w{-}kind($w$; $a$)) $\wedge_{2}$ lnk(w{-}kind($w$; $a$)) = $l$