VasilishinS. A. “Application of the Averaging Method to the Solution of Mixed Problems for Nonlinear Hyperbolic Equations”. Ukrains’kyi Matematychnyi Zhurnal 18, no. 2 (March 5, 1966): 97-102. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8720.