Sakhnovich, L. A. “Spectral Problems for Canonical Systems of Finite-Difference Equations on an Axis”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 49, no. 6, June 1997, pp. 779–788,
https://umj.imath.kiev.ua/index.php/umj/article/view/5062
.