Imash kyzyM., AbdullayevF. G., BushevD. M., and KharkevychY. I. “Isometry of the Subspacesof Solutions of Systems of Differential Equations to the Spaces of Real Functions”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 8, Aug. 2019, pp. 1011-27, https://umj.imath.kiev.ua/index.php/umj/article/view/1494.