\{!$x$:$T$ $\mid$ $P$($x$)\} $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\{$x$:$T$$\mid$ $P$($x$) $\wedge$ ($\forall$$y$:$T$. $P$($y$) $\Rightarrow$ ($y$ = $x$ $\in$ $T$))\}