\begin{tabbing}
w{-}causl($w$; $e$; ${\it e'}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$e$ \+
\\[0ex]rel\_plus(\=w{-}E($w$);\+
\\[0ex]($\lambda$$e$,${\it e'}$. w{-}locl($w$; $e$; ${\it e'}$)
\\[0ex]$\vee$ isrcv(w{-}ekind($w$; ${\it e'}$)) \& $e$ $=$ w{-}sender($w$; ${\it e'}$) $\in$ w{-}E($w$))) ${\it e'}$
\-\-
\end{tabbing}