Proof using.
intros. split.
- omega.
- etransitivity; eauto. apply maxIndex_is_max; auto.
Qed.

(* Specifications: *)
Lemma rachet :
forall x x' xs ys,
eIndex x = eIndex x' ->
In x xs ->
In x' ys ->
In x' xs ->
uniqueIndices xs ->
In x ys.