\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'}$$<$$e$.@${\it e'}$($x$$\rightarrow$es{-}when(${\it es}$; $x$; $e$)) $\wedge$ $\forall$${\it e''}$$\in$(${\it e'}$,$e$].es{-}when(${\it es}$; $x$; ${\it e''}$) = es{-}when(${\it es}$; $x$; $e$) $\in$ $T$
\\[0ex]$\vee$ $\forall$${\it e'}$$\leq$$e$.es{-}when(${\it es}$; $x$; ${\it e'}$) = es{-}when(${\it es}$; $x$; $e$) $\in$ $T$
\end{tabbing}