(ternary) $R$ preserves $P$  $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$x$, $y$, $z$:$T$. $P$($x$) $\Rightarrow$ $P$($y$) $\Rightarrow$ $R$($x$,$y$,$z$) $\Rightarrow$ $P$($z$)