VASILISHIN, S. A. Application of the averaging method to the solution of mixed problems for nonlinear hyperbolic equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 2, p. 97–102, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8720. Acesso em: 7 apr. 2025.