$\forall$${\it es}$:ES, $X$:AbsInterface(Top), $e$:E. ($\uparrow$($e$ $\in_{b}$ le($X$))) $\Leftarrow\!\Rightarrow$ ($\exists$${\it e'}$:E. (${\it e'}$ $\leq$loc $e$  \& ($\uparrow$(${\it e'}$ $\in_{b}$ $X$))))