$\forall$${\it es}$:ES, ${\it as}$, ${\it bs}$:E List.
\\[0ex]loc{-}ordered(${\it es}$;${\it as}$) $\Rightarrow$ loc{-}ordered(${\it es}$;${\it bs}$) $\Rightarrow$ (${\it as}$ $=$ ${\it bs}$ $\Leftrightarrow$ ($\forall$$e$:E. ($e$ $\in$ ${\it as}$) $\Leftrightarrow$ ($e$ $\in$ ${\it bs}$)))