$\forall$${\it es}$:ES, $P$:(E$\rightarrow\mathbb{P}$), $f$:(\{$e$:E$\mid$ $P$($e$)\} $\rightarrow$E). $e$.$f$($e$) is c$<$ preserving on $e$.$P$($e$) $\in$ $\mathbb{P}$