$\forall$$T$:Type, $R$:($T$$\rightarrow$$T$$\rightarrow$Prop), $x$, $y$:$T$. (Sym $x$,$y$:$T$. $x$ $R$ $y$) $\Rightarrow$ ($x$ ($R$$^{\mbox{\scriptsize $\ast$}}$) $y$) $\Rightarrow$ ($y$ ($R$$^{\mbox{\scriptsize $\ast$}}$) $x$)