Case Concerning the Question Whether the Re-evaluation of the German Mark in 1961 and 1969 Constitutes a Case for Application of the Clause in Article 2 (E) of Annex I a of the 1953 Agreement on German External Debts Between Belgium, France, Switzerland, the United Kingdom of Great Britain and Northern Ireland and the United States of America on the One Hand and the Federal Republic of Germany on the Other Decision of 16 May 1980