Yeshkeyev, A.R., and M.T. Omarova. “Сompanions of (n1, n2)-Jonsson Theory”. Bulletin of the Karaganda University. Mathematics Series 96, no. 4 (December 30, 2019): 75–80. Accessed September 4, 2025. http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/338.