EqDecider($T$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$${\it eq}$:($T$$\rightarrow$$T$$\rightarrow\mathbb{B}$) $\times$ ($\forall$$x$,$y$:$T$. ($x$ = $y$) $\Leftarrow\!\Rightarrow$ ($\uparrow$(${\it eq}$($x$,$y$))))