Hrushka, Ya. I. “Base Changeable Sets and Mathematical Simulation of the Evolution of Systems”. Ukrains’kyi Matematychnyi Zhurnal 65, no. 9 (September 25, 2013): 1198–1218. Accessed January 28, 2023. https://umj.imath.kiev.ua/index.php/umj/article/view/2501.