\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]$\vee$ (($\uparrow$isrcv(w{-}ekind($w$; ${\it e'}$))) c$\wedge$ ($e$ = w{-}sender($w$; ${\it e'}$) $\in$ w{-}E($w$))))) ${\it e'}$
\-\-
\end{tabbing}