proposition: Lemma append_assoc : forall s1 s2 s3, (s1 ++ s2 ++ s3 = (s1 ++ s2) ++ s3)%string.
proof: Proof. induction s1; simpl; auto. intros; rewrite IHs1; reflexivity. Qed.
imports: Fiat.Common.Coq__8_4__8_5__Compat Bedrock.Word Coq.ZArith.ZArith Coq.Strings.Ascii Coq.Strings.String Coq.Logic.Eqdep_dec Fiat.Computation.Core Fiat.Computation.FixComp Fiat.Computation.Notations Fiat.Computation.Refinements.General Fiat.Common.DecideableEnsembles Fiat.Narcissus.Common.Specs Fiat.Narcissus.Formats.FixStringOpt Fiat.Narcissus.Formats.NatOpt Fiat.Narcissus.Formats.WordOpt Fiat.Narcissus.Formats.AsciiOpt