proposition: Lemma not_all_lengths n : ~ forall str, length str = n.
proof: Proof. destruct n; intro H; [ destruct (strings_nontrivial 1) as [? H'] | destruct (strings_nontrivial 0) as [? H'] ]; rewrite H in H'; congruence. Qed.
imports: Fiat.Common.Coq__8_4__8_5__Compat Coq.ZArith.ZArith Fiat.Common Fiat.Common.List.Operations Fiat.Common.List.ListFacts Fiat.Common.Le Fiat.Common.Tactics.SetoidSubst Fiat.Common.Tactics.IsClosed Fiat.Parsers.StringLike.Core Fiat.Common.UIP