$\forall$$l_{1}$, $l_{2}$:IdLnk, ${\it tg}_{1}$, ${\it tg}_{2}$:Id. rcv($l_{1}$,${\it tg}_{1}$) $=$ rcv($l_{2}$,${\it tg}_{2}$) $\in$ Knd $\Rightarrow$ \{$l_{1}$ $=$ $l_{2}$ \& ${\it tg}_{1}$ $=$ ${\it tg}_{2}$\}