existse{-}between3(${\it es}$;$e_{1}$;$e_{2}$;$e$.$P$($e$))
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\exists$$e$:es{-}E(${\it es}$). ((es{-}locl(${\it es}$; $e_{1}$; $e$) $\wedge$ es{-}le(${\it es}$; $e$; $e_{2}$)) c$\wedge$ $P$($e$))