Shklyar, A.Y. (1996) “Well-posedness of the cauchy problem for complete second-order operator-differential equations”, Ukrains’kyi Matematychnyi Zhurnal, 48(7), pp. 999–1006. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5272 (Accessed: 5 December 2025).