$\forall$$T$:Type, $R$:($T$$\rightarrow$$T$$\rightarrow$Prop), $x$, $y$:$T$. ($x$ ($R$$^{\mbox{\scriptsize $\ast$}}$) $y$) $\Leftrightarrow$ ($\exists$$z$:$T$. ($x$ ($R$$^{\mbox{\scriptsize $\ast$}}$) $z$) \& ($z$ $R$ $y$)) $\vee$ $x$ $=$ $y$