locl{-}pre{-}preserving(${\it es}$;$f$;$P$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$rel{-}pre{-}preserving(${\it es}$;$f$;$P$;$\lambda$$e$,${\it e'}$. es{-}le(${\it es}$;$e$;${\it e'}$))