YakovetsV. P. (1993) “Asymptotics of the general solution to a linear singularly perturbed system of second-order differential equations with degeneracy”, Ukrains’kyi Matematychnyi Zhurnal, 45(4), pp. 561–575. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5843 (Accessed: 27July2024).