$<\mathbb{B}$,$\wedge_{b}>$ $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$<\mathbb{B}$, $\lambda$$x$,$y$. $x$ =b $y$, $\lambda$$x$,$y$. tt, $\lambda$$x$,$y$. $x$ $\wedge_{b}$ $y$, tt, $\lambda$$x$.$x$$>$