$\forall$${\it es}$:ES, ${\it e'}$:E, $P$:(\{$e$:E$\mid$ loc($e$) = loc(${\it e'}$) $\in$ Id\} $\rightarrow\mathbb{P}$). $\exists$$e$$\leq$${\it e'}$.$P$($e$) $\Leftarrow\!\Rightarrow$ ($P$(${\it e'}$) $\vee$ $\exists$$e$$<$${\it e'}$.$P$($e$))