\begin{tabbing}
R{-}interface($A$;$B$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\forall$$l$:IdLnk, ${\it tg}$:Id.\+
\\[0ex]R{-}da($A$;source($l$))(rcv($l$,${\it tg}$))?Void $\subseteq\rho$ R{-}da($B$;destination($l$))(rcv($l$,${\it tg}$))?Top
\-
\end{tabbing}