AldashevS. A. (1993) “Correctness of multi-dimensional Darboux problems for the wave equation”, Ukrains’kyi Matematychnyi Zhurnal, 45(9), pp. 1299–1306. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5933 (Accessed: 1September2024).