Krul, W.E. “P. Van Hees, G. Puchinger, Briefwisseling Gerretson-Van Eyck”. BMGN - Low Countries Historical Review 100, no. 3 (January 1, 1985): 497–499. Accessed April 25, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-102872.