Koshmanenko, V. D. (2000) “Regularized approximations of singular perturbations from the $H_2$-class”, Ukrains’kyi Matematychnyi Zhurnal, 52(5), pp. 626-637. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4457 (Accessed: 17May2024).