Assanova, A. T. “To the Theory of Nonlocal Problems With Integral Conditions for systems of Equations of Hyperbolic Type”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 70, no. 10, Oct. 2018, pp. 1313-2, https://umj.imath.kiev.ua/index.php/umj/article/view/1637.