Shaldanbayev A.Sh., Shaldanbayeva A.А., и Shaldanbay B.A. «ON PROJECTIONAL ORTHOGONAL BASIS OF A LINEAR NON-SELF -ADJOINT OPERATOR». Academic Scientific Journal of Computer Science, вып. 2, апрель 2019 г., сс. 79-89, https://journals.nauka-nanrk.kz/physics-mathematics/article/view/1182.