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 removeAfterIndex_same_sufficient : forall x l l', sorted l -> sorted l' -> (forall e, eIndex e <= x -> In e l -> In e l') -> (forall e, eIndex e <= x -> In e l' -> In e l) -> removeAfterIndex l' x = removeAfterIndex l x.