ProtasovI. V., and SlobodianiukS. V. “Ultrafilters on Balleans”. Ukrains’kyi Matematychnyi Zhurnal 67, no. 12 (December 25, 2015): 1698-1706. Accessed September 1, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2102.