proposition: Lemma get_drop' {n m str} : get m (drop n str) = get (m + n) str.
proof: Proof. revert str n; induction m; intros. { rewrite <- get_drop; reflexivity. } { rewrite !get_S at 1; rewrite !drop_drop, IHm; simpl. repeat (f_equal; []). omega. } 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