\begin{tabbing}
interface{-}compatible($A$;$B$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\forall$$l$:IdLnk, ${\it tg}$:Id.\+
\\[0ex](interface{-}link($A$;$B$;$l$;${\it tg}$) $\Rightarrow$ $A$(source($l$)).dout($l$,${\it tg}$) $\subseteq\rho$ $B$(destination($l$)).din($l$,${\it tg}$))
\\[0ex]\& (\=interface{-}link($B$;$A$;$l$;${\it tg}$)\+
\\[0ex]$\Rightarrow$ $B$(source($l$)).dout($l$,${\it tg}$) $\subseteq\rho$ $A$(destination($l$)).din($l$,${\it tg}$))
\-\-
\end{tabbing}