proposition: Lemma iffTrans (T : System) (f g h : Formula): SysPrf T (f <-> g)%nt -> SysPrf T (g <-> h)%nt -> SysPrf T (f <-> h)%nt.
proof: Proof. apply (iffTrans LNT). Qed.
imports: Coq(Arith Ensembles List) hydras.Ackermann(Languages folProof folProp folLogic3)