$\forall$$r$:Rng, $b$:$\mathbb{B}$, $p$, $q$:$\mid$$r$$\mid$. (when $b$. ($p$ +$r$ $q$)) $=$ ((when $b$. $p$) +$r$ (when $b$. $q$)) $\in$ $\mid$$r$$\mid$