ВasM. O., and LavrenyukS. P. “On the Uniqueness of a Solution of the Fourier Problem for a System of Sobolev-gal’pern Type”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 48, no. 1, Jan. 1996, pp. 124-8, https://umj.imath.kiev.ua/index.php/umj/article/view/5370.