Section ContextProperties.
Context {L: Language}
{minL: MinimumLanguage L}
{pL: PropositionalLanguage L}
{Gamma: Derivable L}
{bSC: BasicSequentCalculus L Gamma}
{minSC: MinimumSequentCalculus L Gamma}
{ipSC: IntuitionisticPropositionalSequentCalculus L Gamma}
{cpSC: ClassicalPropositionalSequentCalculus L Gamma}.

Lemma classical_derivable_spec: forall (Phi: context) (x: expr),
Phi |-- x <-> ~ consistent (Union _ Phi (Singleton _ (~~ x))).