proposition: Lemma adjacent_err_last: forall g opt_u v, adjacent_err g opt_u (Some v) -> adjacent_last g opt_u v.
proof: Proof. destruct opt_u; intros; apply 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