proposition: Lemma noMiddle (T : System) (f : Formula): SysPrf T (~ f \/ f)%fol.
proof: Proof. unfold orH. Unset Printing Notations. apply impI, nnE, Axm; right; constructor. Set Printing Notations. Qed.
imports: Coq(Ensembles List) hydras.Ackermann(ListExt folProof folProp Deduction)