SakhnovichL. A. “On the Spectral Theory of a Generalized Differential Krein System”. Ukrains’kyi Matematychnyi Zhurnal 52, no. 5 (May 25, 2000): 717-721. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4465.