Avhunbaeva, G.M., E.B. Kurmanov, and E.K. Sabayev. “To the Two-Parameter Theory Gravitational Lenses”. Recent Contributions to Physics 2014, no. 1 (May 21, 2014): 74–79. Accessed February 8, 2026. https://bph.kaznu.kz/index.php/zhuzhu/article/view/762.