Bilusyak, N.I., L. I. Komarnyts’ka, and B. I. Ptashnik. “Dirichlet-Type Problems for Systems of Partial Differential Equations Unresolved With Respect to the Highest Time Derivative”. Ukrains’kyi Matematychnyi Zhurnal 54, no. 12 (December 25, 2002): 1592-1602. Accessed May 13, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4198.