$\forall$${\it es}$:event\_system\{i:l\}, ${\it e'}$:es{-}E(${\it es}$), $P$:(\{$e$:es{-}E(${\it es}$)$\mid$ loc($e$) = loc(${\it e'}$) $\in$ Id\} $\rightarrow$prop\{i:l\}).
\\[0ex]$\exists$$e$$<$${\it e'}$.$P$($e$) $\in$ prop\{i:l\}