$r$ / $d$ $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\langle$Carrier($r$/$d$)$,\,$($\lambda$$x$,$y$. $d$($x$ +$r$ ({-}$r$($y$))))$,\,$($\lambda$$x$,$y$. true$_{2}$)$,\,$+$r$$,\,$(0$r$)$,\,${-}$r$$,\,$($\ast$$r$)$,\,$(1$r$)$,\,$$\div$$r$$\rangle$