proposition: Lemma impTrans (T : System) (f g h : Formula): SysPrf T (f -> g)%fol -> SysPrf T (g -> h)%fol -> SysPrf T (f -> h)%fol.
proof: Proof. intros H H0; apply impI; apply impE with g. - apply sysWeaken, H0. - apply impE with f. + apply sysWeaken, H. + apply Axm; right; constructor. Qed.
imports: Coq(Ensembles List) hydras.Ackermann(ListExt folProof folProp Deduction)