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$\forall$$T$:Type, ${\it eq}$:EqDecider($T$), ${\it es}$:event\_system\{i:l\}, $x$:Id, $e$:\{\=$e$:es{-}E(${\it es}$)$\mid$ \+
\\[0ex]es{-}dtype(${\it es}$; loc($e$); $x$; $T$)\} .
\-\\[0ex]($\uparrow$$x$ changed before $e$) $\Leftarrow\!\Rightarrow$ $\exists$${\it e'}$$<$$e$.$\neg$(es{-}after(${\it es}$; $x$; ${\it e'}$) = es{-}when(${\it es}$; $x$; ${\it e'}$) $\in$ $T$)
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