$\forall$$g$:Mon, $b$, ${\it b'}$:$\mathbb{B}$, $p$:$\mid$$g$$\mid$. (when $b$. when ${\it b'}$. $p$) = (when $b$ $\wedge_{b}$ ${\it b'}$. $p$) $\in$ $\mid$$g$$\mid$