Ltac use_entries_match :=
    match goal with
      | [ _ : eIndex ?e1 = eIndex ?e2,
              H : context [entries_match]
                              |- _ ] =>
        first [ solve [eapply H with (e:=e2)(e':=e1); eauto; congruence] |
                solve [eapply H with (e:=e1)(e':=e2); eauto; congruence]]
    end.

Lemma contiguous_index_adjacent : forall l i a b, sorted (a :: b :: l) -> contiguous_range_exact_lo (a :: b :: l) i -> eIndex a = S (eIndex b) /\ eIndex a > i.