\begin{tabbing}
$\forall$${\it es}$:event\_system\{i:l\}, $x$:Id, $e$:es{-}E(${\it es}$).
\\[0ex]($\uparrow$es{-}isconst(${\it es}$; loc($e$); $x$))
\\[0ex]$\Rightarrow$ guard(\=(constant\_function(\=es{-}state{-}ap(es\_state\_when(${\it es}$; $e$); $x$);\+\+
\\[0ex]rationals;
\\[0ex]es{-}vartype(${\it es}$; loc($e$); $x$))
\-\\[0ex]$\wedge$ constant\_function(\=es{-}state{-}ap(es\_state\_after(${\it es}$; $e$); $x$);\+
\\[0ex]rationals;
\\[0ex]es{-}vartype(${\it es}$; loc($e$); $x$))))
\-\-
\end{tabbing}