Andrusyak, R.V., V.M. Kyrylych, and Peliushkevych О.V. “A Problem for Degenerated Semilinear Hyperbolic System in Sector”. Carpathian Mathematical Publications 3, no. 2 (December 29, 2011): 4–12. Accessed November 21, 2024. https://journals.pnu.edu.ua/index.php/cmp/article/view/3060.