New York, 12 March 1956 - Institutional correspondence Bernard Karpel's letter to Willem Sandberg, dated 12 March 1956
New York, 27 November 1956 - Institutional correspondence Bernard Karpel's letter to Willem Sandberg, dated 27 November 1956
Madrid, 7 and 19 January 1981 - Institutional correspondence A letter from Enrique Calduch to Javier Tusell