Sokil, B. I. “On Asymptotic Approximation of a Solution of a Boundary-Value Problem for a Nonlinear Nonautonomous Equation”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 11 (November 25, 1997): 1580–1583. Accessed May 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5160.