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 sorted_app_gt : forall l1 l2 e1 e2, sorted (l1 ++ l2) -> In e1 l1 -> In e2 l2 -> eIndex e1 > eIndex e2.