$\forall$$E$,$X_{1}$,$X_{2}$:Type, ${\it info}$:($E$$\rightarrow$((:Id $\times$ $X_{1}$) + (:(:IdLnk $\times$ $E$) $\times$ $X_{2}$))), $e$:$E$.
\\[0ex]($\uparrow$rcv?($e$)) $\Rightarrow$ (sender($e$) $\in$ $E$)