Y. Trukhan and M. M. Sheremeta, “Boundedness of the l-Index of the Naftalevich–Tsuji Product”, Ukr. Mat. Zhurn., vol. 56, no. 2, pp. 247–256, Feb. 2004, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3748