Beyen, M. “L.H. Maas, Pro Patria. Werken, Leven En Streven Van Gerrit Kalff 1856-1923”. BMGN - Low Countries Historical Review 115, no. 1 (January 1, 2000): 148–150. Accessed November 21, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-105951.