New York, 10 February 1956 - Institutional correspondence A letter from Louise A. Boyer to Petro (Nelly) Van Doesburg
20 February 1980 - Institutional correspondence A letter from Ricardo de la Cierva Hoces to Adolfo Suárez
Madrid, 28 June 1980 - Institutional correspondence Ricardo de la Cierva Hoces' letter to Javier Tusell