Murach, A. A., O. B. Pelekhata, and V. O. Soldatov. “Approximation Properties of Solutions to Multipoint Boundary-Value Problems”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 73, no. 3, Mar. 2021, pp. 341 -53, doi:10.37863/umzh.v73i3.6505.