Zurich, 12 December 1955 - Institutional correspondence A letter from Klaus Herdeg to Willem Sandberg
12 September 1981 - Newspapers Protests in the Basque Country over the installation of Guernica in the Casón del Buen Retiro
<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)