$\forall$${\it es}$:ES, $p$:(E$\rightarrow$(E + Top)). causal{-}predecessor(${\it es}$;$p$) $\Rightarrow$ ($\forall$$e$, ${\it e'}$:E. $e$ $p$$<$ ${\it e'}$ $\Rightarrow$ ($e$ $<$ ${\it e'}$))