IMASH KYZY, M.; ABDULLAYEV, F. G.; BUSHEV, D. M.; KHARKEVYCH, Y. I. Isometry of the subspacesof solutions of systems of differential equations to the spaces of real functions. Ukrains’kyi Matematychnyi Zhurnal, v. 71, n. 8, p. 1011-1027, 25 Aug. 2019.