M. T. Karaev and N. S. Iskenderov, “Berezin number of operators and related questions”, MFAT, vol. 19, no. 1, pp. 68–72, Mar. 2013, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/536