Aldashev, S. A. “Well-Posedness of Mixed Problems for Multidimensional Hyperbolic Equations With Wave Operator”. Ukrains’kyi Matematychnyi Zhurnal 69, no. 7 (July 25, 2017): 992–999. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/1752.