Jansen, H.P.H. “In Memoriam Dr. H. Zwager (1926-1973)”. BMGN - Low Countries Historical Review 90, no. 1 (January 1, 1975): 83–85. Accessed May 5, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-107748.