Zurich, 12 December 1955 - Institutional correspondence A letter from Klaus Herdeg to Willem Sandberg
Madrid, 11 December 1979 - Institutional correspondence Marcelino Oreja's letter to Manuel Clavero Arévalo
Homenaje a Picasso... Mucha luz se ha perdido - Lithograph Omaggio a Picasso... Molta luce è andata perduta