\begin{tabbing}
$\forall$$L$:MsgA List, $l$:IdLnk, ${\it tg}$:Id.
\\[0ex]($\forall$$A$,$B$$\in$$L$.$A$ $\Vert\!+$ $B$)
\\[0ex]$\Rightarrow$ (\=rcv($l$,${\it tg}$) declared in $\oplus$($L$)\+
\\[0ex]$\Leftrightarrow$
\\[0ex]reduce($\lambda$$M$,$x$. rcv($l$,${\it tg}$) $\in$ dom(1of(2of($M$))) $\vee_{2}$ $x$;false$_{2}$;$L$))
\-
\end{tabbing}