$\forall$$l$:IdLnk, ${\it da}$:$k$:Knd fp$\rightarrow$ Type, ${\it tg}$:Id. ${\it tg}$ $\in$ dom(dt($l$;${\it da}$)) $\Leftrightarrow$ rcv($l$,${\it tg}$) $\in$ dom(${\it da}$)