Vasilishin, S.A. (1966) “Application of the averaging method to the solution of mixed problems for nonlinear hyperbolic equations”, Ukrains’kyi Matematychnyi Zhurnal, 18(2), pp. 97–102. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8720 (Accessed: 7 April 2025).