New York, 10 February 1956 - Institutional correspondence A letter from Louise A. Boyer to Petro (Nelly) Van Doesburg
Madrid, 29 May and 10 June 1981 - Institutional correspondence A letter from Felipe Cons Gorostola to Álvaro Martínez Novillo, and reply
2 December 1938 - Institutional correspondence The National Committee for Spanish Aid's letter to Pablo Picasso