A/RES/58/232 Article 18 United Nations laissez-passer Officials of the World Tourism Organization shall be entitled, in accordance with such special arrangements as may be concluded between the Secretary-General of the United Nations and the Secretary-General of the World Tourism Organization, to use laissez-passer of the United Nations. Article 19 Implementation of the Agreement The Secretary-General of the United Nations and the Secretary-General of the World Tourism Organization may enter into such supplementary arrangements for the implementation of the present Agreement as may be found desirable. Article 20 Amendment and revision The present Agreement may be amended or revised by agreement between the United Nations and the World Tourism Organization, and any such amendment or revision shall come into force on its approval by the General Assembly of the United Nations and the General Assembly of the World Tourism Organization. Article 21 Entry into force The present Agreement enters into force on its approval by the General Assembly of the United Nations and the General Assembly of the World Tourism Organization. 8