Syrovatskyi, V. N. “Functional Models of Commutative Systems of Operators Close to the Unitary”. Visnyk of V. N. Karazin Kharkiv National University. Ser. Mathematics, Applied Mathematics and Mechanics, no. 1081, Dec. 2013, pp. 54-66, doi:10.26565/2221-5646-2013-1081-06.