proposition: Corollary adjacent_requires_vvalid: forall g u v, adjacent g u v -> vvalid g u /\ vvalid g v.
proof: Proof. intros. destruct H. apply (adj_edge_vvalid g x u v H). Qed.
imports: Coq.Logic.Classical CertiGraph.lib.List_ext CertiGraph.lib.EquivDec_ext CertiGraph.graph.graph_model CertiGraph.graph.graph_relation CertiGraph.graph.path_lemmas CertiGraph.graph.graph_gen CertiGraph.graph.FiniteGraph