ZhuravlevV. F., ZabrodskiyP. N., and FominN. P. “Conditions of Solvability and representation of the Solutions of Equations With Operator Matrices”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 4, Apr. 2019, pp. 471-85, http://umj.imath.kiev.ua/index.php/umj/article/view/1452.