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causale{-}order{-}preserving(${\it es}$;$a$.$f$($a$);$e$.$P$($e$))
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\forall$$e$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} , ${\it e'}$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} .\+
\\[0ex]es{-}causle(${\it es}$;$e$;${\it e'}$) $\Rightarrow$ es{-}causle(${\it es}$;$f$($e$);$f$(${\it e'}$))
\-
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