$\forall$$k$:Knd, $l$:IdLnk, ${\it tg}$:Id. ($\uparrow$isrcv($k$)) $\Rightarrow$ (lnk($k$) = $l$) $\Rightarrow$ (tag($k$) = ${\it tg}$) $\Rightarrow$ (rcv($l$,${\it tg}$) = $k$)