W.J.M. Klaassen, De progressieve samenwerking van PvdA, D’66, PPR en PSP, 1966-1977. BMGN - Low Countries Historical Review, [S. l.], v. 118, n. 2, p. 283–284, 2003. DOI: 10.18352/bmgn-lchr.5877. Disponível em: https://ojstest.minions.amsterdam/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-106745.. Acesso em: 2 jul. 2024.