Mitropolskiy YA, Khoma LG. The existence of a classical solution to the mixed problem for a linear second-order hyperbolic equation. Ukr. Mat. Zhurn. [Internet]. 1993Sep.25 [cited 2024Jul.27];45(9):1232–1238. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/5925