proposition: Lemma length_firstn_skipn_app'' {A} : forall (n m o : nat) (l : list A), length l = n + m + o -> length (firstn n l) = n.
proof: Proof. induction n; destruct l; simpl; intros; try discriminate; eauto. Qed.
imports: Fiat.Common.Coq__8_4__8_5__Compat Coq.Bool.Bool Coq.ZArith.ZArith Coq.Lists.List Fiat.Common.DecideableEnsembles Fiat.Common.EnumType Fiat.Common.BoundedLookup Fiat.Common Fiat.Common.ilist Fiat.Common.Tactics.CacheStringConstant Fiat.Common.IterateBoundedIndex Fiat.Computation Bedrock.Word