$\forall$$T$:Type, $E$:($T$$\rightarrow$$T$$\rightarrow\mathbb{P}$).
\\[0ex]EquivRel($T$;$x$,$y$.$E$($x$,$y$)) $\Rightarrow$ ($\forall$$a$, $b$:$T$. ($a$ = $b$ $\in$ ($x$,$y$:$T$//$E$($x$,$y$))) $\Leftarrow\!\Rightarrow$ ($\downarrow$$E$($a$,$b$)))