\begin{tabbing}
IsIntegDom($r$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=0$r$ $\neq$ 1$r$ $\in$ $\mid$$r$$\mid$ \+
\\[0ex]\& (\=$\forall$$u$:$\mid$$r$$\mid$, $v$:$\mid$$r$$\mid$.\+
\\[0ex]($\neg$($v$ = (0$r$) $\in$ $\mid$$r$$\mid$)) $\Rightarrow$ (($u$ ($\ast$$r$) $v$) = (0$r$) $\in$ $\mid$$r$$\mid$) $\Rightarrow$ ($u$ = (0$r$) $\in$ $\mid$$r$$\mid$))
\-\-
\end{tabbing}