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