London, 18 April 1980 - Institutional correspondence Nicholas Serota's letter to Roland Penrose, dated 18 April 1980
London, 1 May 1980 - Institutional correspondence Nicholas Serota's letter to Roland Penrose, dated 1 May 1980
Oslo, 27 November 1956 - Institutional correspondence A letter from Miguel de Aldasoro to Alberto Martín-Artajo Álvarez