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 thing3 : forall l l' e, sorted (l ++ l') -> (forall e', In e' (l ++ l') -> eIndex e' > 0) -> In e (l ++ l') -> eIndex e <= maxIndex l' -> In e l'.