BilusyakN.; Komarnyts’kaL. I.; PtashnikB. I. Dirichlet-Type Problems for Systems of Partial Differential Equations Unresolved with Respect to the Highest Time Derivative. Ukrains’kyi Matematychnyi Zhurnal, v. 54, n. 12, p. 1592-1602, 25 Dec. 2002.