Yeshkeyev, A.R. “About Central Types and the Cosemanticness of the ∆-PM Fragment of the Jonsson Set”. Bulletin of the Karaganda University. Mathematics Series 87, no. 3 (September 29, 2017): 51–58. Accessed March 7, 2026. https://mts.buketov.edu.kz/mathematics-vestnik/article/view/167.