Il'man, V. M., and V. E. Kapustyan. “Singularities of Solutions of Singular Integral Equations”. Ukrains’kyi Matematychnyi Zhurnal, vol. 54, no. 10, Oct. 2002, pp. 1429-36, https://umj.imath.kiev.ua/index.php/umj/article/view/4180.