\begin{tabbing}
R{-}interface($A$; $B$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\forall$$l$:IdLnk, ${\it tg}$:Id.\+
\\[0ex]subtype\_rel(\=fpf{-}cap(R{-}da($A$; source($l$)); Kind{-}deq; rcv($l$,${\it tg}$); void);\+
\\[0ex]fpf{-}cap(R{-}da($B$; destination($l$)); Kind{-}deq; rcv($l$,${\it tg}$); top))
\-\-
\end{tabbing}