proposition: Lemma ext_app: forall h1 h2, ext_hist (h1 ++ h2) = (ext_hist h1) ++ (ext_hist h2).
proof: Proof. intros. unfold ext_hist. apply map_app. Qed.
imports: Coq(FunctionalExtensionality Arith Lia) Coq(Arith.Peano_dec Arith.Compare_dec) Coq(Relations.Relation_Operators) Coq(List) Chapar(Predefs)