AskarovM. “On the Rate of Convergence of Methods of Projection-Iterative Type for Fredholm Equations With Periodic Analytic Kernels”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 47, no. 9, Sept. 1995, pp. 1155–1161, https://umj.imath.kiev.ua/index.php/umj/article/view/5514.