Y. M. Arlinskii and Y. Kovalev, “Factorizations of nonnegative symmetric operators”, MFAT, vol. 19, no. 3, pp. 211–226, Sep. 2013, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/549