proposition: Lemma last_err_app: forall {A:Type} (l1 l2: list A) (a: A), last_error l2 = Some a -> last_error (l1++l2) = Some a.
proof: Proof. intros. apply (last_err_app' l2 l1 a H). Qed.
imports: Coq.Lists.List Coq.micromega.Lia Coq.Sorting.Permutation Coq.ZArith.ZArith_base Coq.ZArith.Zcomplements Coq.Logic.FunctionalExtensionality CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext VST.zlist.sublist VST.zlist.list_solver