Proof using.
intros.
induction l; simpl in *; intuition; repeat subst; auto;
find_apply_hyp_hyp; intuition.
Qed.

Lemma contiguous_app_prefix_2 :
forall l l' l'' i,
sorted (l ++ l') ->
contiguous_range_exact_lo (l ++ l') 0 ->
Prefix l' l'' ->
maxIndex l'' < i <= maxIndex l ->
exists e, eIndex e = i /\ In e l.