proposition: Lemma RFG_reachable_decicable': forall (g: PreGraph V E) {rfg: ReachableFiniteGraph g} x y, Decidable (vvalid g x) -> Decidable (reachable g x y).
proof: Proof. intros. destruct H; [apply RFG_reachable_decicable; auto | right]. intro. apply reachable_head_valid in H; tauto. Qed.
imports: CertiGraph.lib.Coqlib CertiGraph.lib.EnumEnsembles CertiGraph.lib.EquivDec_ext CertiGraph.lib.List_ext CertiGraph.lib.relation_list CertiGraph.lib.Equivalence_ext CertiGraph.graph.graph_model CertiGraph.graph.graph_gen CertiGraph.graph.path_lemmas