G. Avhunbaeva, E. Kurmanov, and E. Sabayev, “To the two-parameter theory gravitational lenses”, Rec.Contr.Phys., vol. 48, no. 1, pp. 74–79, May 2014, Accessed: Sep. 21, 2026. Available: https://bph.kaznu.kz/index.php/zhuzhu/article/view/762