S. A. Plaksa, “On the composition of operators in vector spaces and their Noether property”, Ukr. Mat. Zhurn., vol. 45, no. 8, pp. 1177–1180, Aug. 1993, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5918