Stockholm, 23 October 1956 - Institutional correspondence A letter from Bo Wennberg and K. G. Hulten to Pablo Picasso
Chicago, 11 October 1939 - Institutional correspondence Charles Goodspeed's telegram to Pablo Picasso
Gerti Fietzek (ed.), Cologne: Buchhandlung Walther König, 2009 - Essay Maria Eichhorn. The Artist's Contract