Stockholm, 23 October 1956 - Institutional correspondence Ernesto de Zulueta's letter to Alberto Martín-Artajo Álvarez
Brussels, 14 May 1956 - Institutional correspondence A letter from the Spanish ambassador in Belgium to Alberto Martín-Artajo Álvarez
Amsterdam, 6 July 1956 - Institutional correspondence A letter from J. M. Trias de Bes to Alberto Martín-Artajo Álvarez