Petrenko, O.V. and Protasov, I.V. (2012) “Balleans and G -spaces”, Ukrains’kyi Matematychnyi Zhurnal, 64(3), pp. 344–350. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/2580 (Accessed: 5 December 2025).