Ashyralyev, Allaberen, and Makhmud A. Sadybekov. “Preface”. Bulletin of the Karaganda University. Mathematics Series 99, no. 3 (September 30, 2020): 4. Accessed September 5, 2025. http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/451.