$\forall$${\it es}$:ES, $e$:E, $l$:IdLnk, ${\it tg}$:Id. \\[0ex]kind($e$) $=$ rcv($l$,${\it tg}$) $\in$ Knd \\[0ex]$\Rightarrow$ \{loc($e$) $=$ destination($l$) $\in$ Id \& loc(sender($e$)) $=$ source($l$) $\in$ Id\}