$\forall$$E$, $X_{1}$, $X_{2}$:Type, ${\it info}$:($E$$\rightarrow$(Id$\times$$X_{1}$+(IdLnk$\times$$E$)$\times$$X_{2}$)), $e$:$E$. rcv?($e$) $\Rightarrow$ sender($e$) $\in$ $E$