Kossmann, E.H. “P. Van Hees, Bibliografie Van P. Geyl”. BMGN - Low Countries Historical Review 88, no. 3 (January 1, 1973): 472–473. Accessed February 7, 2023. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-101936.