Proof using.
induction l1; intros; simpl in *; intuition.
subst. destruct l2; simpl in *; auto.
specialize (H2 e0); conclude_using eauto; intuition.
Qed.

(* Specifications: *)
Lemma findGtIndex_Prefix :
forall l i,
Prefix (findGtIndex l i) l.
Lemma findGtIndex_Prefix :
forall l i,
Prefix (findGtIndex l i) l.