Pavlyuk, In.I., and S.V. Sudoplatov. “Families of Theories of Abelian Groups and Their Closures”. Bulletin of the Karaganda University-Mathematics 92, no. 4 (December 29, 2018): 72–78. Accessed June 27, 2026. https://mts.buketov.edu.kz/mathematics-vestnik/article/view/242.