proposition: Lemma drop_drop : forall n m l, drop n (drop m l) = drop (n+m) l.
proof: Proof. Proof using. intros n. induction m; simpl; intros. { rew_nat*. } { destruct l as [|x l']. { repeat rewrite drop_nil. auto. } { rewrite drop_cons_pos; try math. rew_nat*. } } Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)