proposition: Lemma orSys (T : System) (f g h : Formula): SysPrf (Ensembles.Add T f) h -> SysPrf (Ensembles.Add T g) h -> SysPrf (Ensembles.Add T (f \/ g)%fol) h.
proof: Proof. intros H H0; eapply orE. - apply Axm; right; constructor. - apply sysWeaken, impI; assumption. - apply sysWeaken, impI; assumption. Qed.
imports: Coq(Ensembles List) hydras.Ackermann(ListExt folProof folProp Deduction)