Letter dated 2009/04/20 from the Permanent Representative of the Russian Federation and the Charge d'Affaires of the Permanent Mission of the United States of America to the Conference on Disarmanent addressed to the Secretary-General of the Conference transmitting the text of the joint statement by Mr. Dmitriy A. Medvedev, President of the Russian Federation and Mr. Barack Obama, President of the United States of America, made in London on 1 April 2009