Yeshkeyev, A.R., Issaeva А.К., and N.V. Popova. “Сore Jonsson Theories”. Bulletin of the Karaganda University. Mathematics Series 97, no. 1 (March 30, 2020): 104–110. Accessed October 14, 2025. https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/327.