Alt, H. “Platonisme, Konseptualisme En Nomimalisme in Die Versamelingsteorie”. Tydskrif Vir Christelike Wetenskap | Journal for Christian Scholarship, vol. 57, no. 3&4, Dec. 2021, pp. 31 -52, https://pubs.ufs.ac.za/index.php/tcw/article/view/557.