This Convention shall not abrogate multilateral or bilateral
conventions or arrangements in effect between two or more Contracting
States. In the event of any difference between the provisions of such
existing conventions or arrangements and the provisions of this
Convention, the provisions of this Convention shall prevail. Rights in
works acquired in any Contracting State under existing conventions or
arrangements before the date on which this Convention comes into force
in such State shall not be affected. Nothing in this Article shall
affect the provisions of Articles XVII and XVIII.