P. van der Steen, Cals, koopman in verwachtingen 1914-1971. BMGN-LCHR [Internet]. 2006 Jan. 1 [cited 2024 Jul. 2];121(2):366-8. Available from: https://ojstest.minions.amsterdam/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-107939