\begin{tabbing}
pred!($E$;${\it pred?}$;${\it info}$;$e$;${\it e'}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=(($\neg$($\uparrow$first(${\it pred?}$;${\it e'}$))) c$\wedge$ ($e$ = pred(${\it pred?}$;${\it e'}$) $\in$ $E$))\+
\\[0ex]$\vee$ (($\uparrow$rcv?(${\it info}$;${\it e'}$)) c$\wedge$ ($e$ = sender(${\it info}$;${\it e'}$) $\in$ $E$))
\-
\end{tabbing}