$a$ = !$x$:$T$. $Q$($x$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$Q$($a$) $\wedge$ ($\forall$${\it a'}$:$T$. $Q$(${\it a'}$) $\Rightarrow$ (${\it a'}$ = $a$ $\in$ $T$))