Roxbury, 22 November 1955 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 22 November 1955
Roxbury, 12 January 1956 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 12 January 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)