\begin{tabbing}
causally{-}related(${\it es}$;$e$.$P$($e$);${\it e'}$.$Q$(${\it e'}$);$R$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\exists$\=$f$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} $\rightarrow$\{$e$:es{-}E(${\it es}$)$\mid$ $Q$($e$)\} \+
\\[0ex]causal{-}bijection(${\it es}$;$a$.$f$($a$);$e$.$P$($e$);${\it e'}$.$Q$(${\it e'}$);$R$)
\-
\end{tabbing}