Roxbury, 22 November 1955 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 22 November 1955
Roxbury, 12 January 1956 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 12 January 1956
New York, 8 April 1981 - Press release and communication A press release from New York's Museum of Modern Art concerning a Spanish delegation's request to send Guernica to Spain