antecedent{-}function(${\it es}$;$P$;$Q$;$f$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$e$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} . es{-}causl(${\it es}$; ($f$($e$)); $e$) \& $Q$($f$($e$))