DerkachV. A. “On Schur–Nevanlinna–Pick Indefinite Interpolation Problem”. Ukrains’kyi Matematychnyi Zhurnal 55, no. 10 (October 25, 2003): 1299-1315. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4004.