basic
\\[0ex]Cancel($T$;$S$;${\it op}$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$u$:$T$, $v$:$T$, $w$:$S$. (($w$ ${\it op}$ $u$) = ($w$ ${\it op}$ $v$) $\in$ $T$) $\Rightarrow$ ($u$ = $v$ $\in$ $T$)