$\forall$$l_{1}$, $l_{2}$:IdLnk, ${\it dt}$:${\it tg}$:Id fp$\rightarrow$ Type, ${\it tg}$:Id, $T$:Type.
\\[0ex]lnk{-}decl($l_{1}$;${\it dt}$)(rcv($l_{2}$,${\it tg}$))?$T$ $\sim$ if $l_{1}$ = $l_{2}$$\rightarrow$ ${\it dt}$(${\it tg}$)?$T$ else $T$ fi