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
28 February 1974 - Press release and communication The artist Tony Shafrazi has freed Guernica from its chains of ownership and has returned its revolutionary nature