\begin{tabbing}
$\forall$${\it tg}$:Id, $l$:IdLnk, $L$:MsgA List.
\\[0ex]($\forall$$A$,$B$$\in$$L$.$A$ $\Vert\!+$ $B$)
\\[0ex]$\Rightarrow$ (\=$\oplus$($L$).din($l$,${\it tg}$)\+
\\[0ex]$\sim$
\\[0ex]reduce($\lambda$$M$,$x$. if rcv($l$,${\it tg}$) $\in$ dom(1of(2of($M$)))$\rightarrow$ $M$.din($l$,${\it tg}$) else $x$ fi;Top;$L$))
\-
\end{tabbing}