Abma, R. “Het Plan Van De Arbeid En De SDAP”. BMGN - Low Countries Historical Review 92, no. 1 (January 1, 1977): 37–68. Accessed April 26, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-102130.