returns UV = all respected U->Ux in ternary coding (1=V,2=U)

def UV_B(self):
        """
        returns UV = all respected U->Ux in ternary coding (1=V,2=U)
        """
        h = reduce(lambda x,y:x&y,(B(g,self.width-1) for g in self))
        return UV_B(h, self.width)