PHILIPS, J. W.J. Formsma, Historie van Groningen. Stad en land. BMGN - Low Countries Historical Review, [S. l.], v. 92, n. 2, p. 308–310, 1977. DOI: 10.18352/bmgn-lchr.1990. Disponível em: https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-102154. Acesso em: 7 feb. 2023.