proposition: Lemma hd_error_app: forall {A:Type} (l2 l1: list A) (a: A), hd_error l1 = Some a -> hd_error (l1++l2) = Some a.
proof: Proof. induction l1; intros. inversion H. simpl. simpl in H. auto. 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