Brussels, 14 May 1956 - Institutional correspondence A letter from the Spanish ambassador in Belgium to Alberto Martín-Artajo Álvarez
New York, 7 March 1956 - Institutional correspondence William S. Lieberman's letter to Porter McCrary
New York, 20 September 1956 - Institutional correspondence William S. Lieberman's letter to Alfred H. Barr Jr.
New York, 5 July 1956 - Institutional correspondence William S. Lieberman's letter to Richard Griffith