RomanyukV. S. 2001. “Estimates of the Kolmogorov Widths of Classes of Analytic Functions Representable by Cauchy-Type Integrals. II”. Ukrains’kyi Matematychnyi Zhurnal 53 (3), 346-55. https://umj.imath.kiev.ua/index.php/umj/article/view/4257.