Roiter, A. V., and V. V. Sergeychuk. “Existence of a Multiplicative Basis for a Finitely Spaced Module over an Aggregate”. Ukrains’kyi Matematychnyi Zhurnal, vol. 46, no. 5, May 1994, pp. 567–579, https://umj.imath.kiev.ua/index.php/umj/article/view/5719.