Kasymov, K. A., and D. N. Nurgabyl. “Asymptotic Behavior of Solutions of Linear Singularly Perturbed General Separated Boundary-Value Problems With Initial Jump”. Ukrains’kyi Matematychnyi Zhurnal, vol. 55, no. 11, Nov. 2003, pp. 1476-88, https://umj.imath.kiev.ua/index.php/umj/article/view/4018.