\begin{tabbing}
match($l$;$t$;${\it t'}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\parallel$snds($l$;$t$)$\parallel\leq_{2}\parallel$rcvs($l$;${\it t'}$)$\parallel$\+
\\[0ex]$\wedge_{2}$ $\parallel$rcvs($l$;${\it t'}$)$\parallel<_{2}\parallel$snds($l$;$t$)$\parallel$+$\parallel$onlnk($l$;m(source($l$);$t$))$\parallel$
\-
\end{tabbing}