$\forall$${\it da}$:$k$:Knd fp$\rightarrow$ Type, $l$:IdLnk, ${\it tg}$:Id, $T$:Top. dt($l$;${\it da}$)(${\it tg}$)?$T$ $\sim$ ${\it da}$(rcv($l$,${\it tg}$))?$T$