WellFnd\{i\}($A$;$x$,$y$.$R$($x$;$y$))
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$P$:($A$$\rightarrow\mathbb{P}$). ($\forall$$j$:$A$. ($\forall$$k$:$A$. $R$($k$;$j$) $\Rightarrow$ $P$($k$)) $\Rightarrow$ $P$($j$)) $\Rightarrow$ \{$\forall$$n$:$A$. $P$($n$)\}