Q{-}R{-}pre{-}preserving(${\it es}$;$f$;$P$;$Q$;$R$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$e$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} , ${\it e'}$:\{$e$:es{-}E(${\it es}$)$\mid$ $P$($e$)\} . ($Q$($f$($e$),$f$(${\it e'}$))) $\Rightarrow$ ($R$($e$,${\it e'}$))