“H.J. Langeveld, Protestants En Progressief. De Christelijk-Democratiesche Unie 1926-1946”. BMGN - Low Countries Historical Review 108, no. 3 (January 1, 1993): 530–532. Accessed November 23, 2024. https://ojstest.minions.amsterdam/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-104313.