KharibegashviliS. S., and MidodashviliB. G. “Boundary-Value Problem for a Class of Nonlinear Systems of Partial Differential Equations of Higher Orders”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 74, no. 6, July 2022, pp. 856 -8, doi:10.37863/umzh.v74i6.6968.