V. F. Zhuravlev, “Solvability criterion and representation of solutions of $n$-normal and $d$-normal linear operator equations in a Banach space”, Ukr. Mat. Zhurn., vol. 62, no. 2, pp. 167–182, Feb. 2010, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2853