Kungozhin, A M. “Description of Positively Existentially Closed Models in Any Class of -Structures With Unary Predicates Axiomatizable by Any H-Universal Sentence”. Journal of Mathematics, Mechanics and Computer Science 69, no. 2 (June 28, 2011): 39–43. Accessed January 31, 2026. https://bm.kaznu.kz/index.php/kaznu/article/view/193.