proposition: Lemma adj_edge_sym: forall g e u v, adj_edge g e u v -> adj_edge g e v u.
proof: Proof. intros. destruct H. split; auto. destruct H0. right; auto. left; auto. 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