$\vdash$  $\forall$$T$:Type, $E$:($T$$\rightarrow$$T$$\rightarrow\mathbb{P}$). EquivRel($T$;$x$,$y$.$E$($x$,$y$)) $\Rightarrow$ ($\forall$$a$, $b$:$T$. ($a$ = $b$) $\Leftarrow\!\Rightarrow$ ($\downarrow$$E$($a$,$b$)))