Section TheoryOfSequentCalculus.
Context {L: Language}
{Gamma: Derivable L}.

Lemma DeductionWeaken_DerivableFiniteWitnessed_2_ContextualDerivableFiniteWitnessed:
DeductionWeaken L Gamma ->
DerivableFiniteWitnessed L Gamma ->
ContextualDerivableFiniteWitnessed L Gamma.