BilusyakN. and PtashnikB. I. (2001) “Boundary-Value Problem for Weakly Nonlinear Hyperbolic Equations with Variable Coefficients”, Ukrains’kyi Matematychnyi Zhurnal, 53(9), pp. 1281-1286. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4347 (Accessed: 27July2024).