proposition: Lemma orI2 (T : System) (f g : Formula): SysPrf T g -> SysPrf T (f \/ g)%fol.
proof: Proof. intros h; unfold orH; apply impI, sysWeaken; assumption. Qed.
imports: Coq(Ensembles List) hydras.Ackermann(ListExt folProof folProp Deduction)