$e_{2}$ = first $e$ $\geq$ $e_{1}$.$P$($e$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$e_{1}$ $\leq$ $e_{2}$  \& $P$($e_{2}$) \& $\forall$$e$$\in$[$e_{1}$,$e_{2}$).$\neg$$P$($e$)