Proof using.
red. intuition.
- exists x. intuition. simpl in *. inv H2; [reflexivity | omega].
- simpl in *. intuition. subst. omega.
Qed.

Lemma contiguous_adjacent_sufficient :
forall x y l i,
eIndex x = S (eIndex y) ->
contiguous_range_exact_lo (y :: l) i ->
contiguous_range_exact_lo (x :: y :: l) i.