SakhnovichL. A. “Spectral Problems for Canonical Systems of Finite-Difference Equations on an Axis”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 6 (June 25, 1997): 779–788. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5062.