V. A. Derkach, S. Hassi, and H. de Snoo, “Operator models associated with Kac subclasses of generalized Nevanlinna functions”, MFAT, vol. 5, no. 1, pp. 65–87, Mar. 1999, Accessed: Dec. 18, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/81