 But axioms can’t have free variables under the Quinean conception and, hence, that proof is not available. Likewise, the de re validity \(\forall \sfx\,\Box(\Box \sfF\sfx \to \sfF\sfx)\) is proved in SQML by applying the rule of Necessitation to the T instance \(\Box \sfF\sfx \to \sfF\sfx\) and then generalizing: