New York, 12 March 1956 - Institutional correspondence Bernard Karpel's letter to Willem Sandberg, dated 12 March 1956
New York, 27 November 1956 - Institutional correspondence Bernard Karpel's letter to Willem Sandberg, dated 27 November 1956
<em>El País</em>, January 21, 2016 - Article “El fiasco de la Bienal de Arte de Sevilla acaba en condena” (The fiasco of the Art Biennial of Seville ends up with a sentence)