Kotsur, I. M., and M. F. Kotsur. 1996. “On the Radii of Convexity and Starlikeness for Some Special Classes of Analytic Functions in a Disk”. Ukrains’kyi Matematychnyi Zhurnal 48 (7): 954-58. https://umj.imath.kiev.ua/index.php/umj/article/view/5268.