Hatamleh, R., and V. A. Zolotarev. 2016. “Triangular Models of Commutative Systems of Linear Operators Close to Unitary Operators”.
Ukrains’kyi Matematychnyi Zhurnal
68 (5): 694-711.
https://umj.imath.kiev.ua/index.php/umj/article/view/1872
.