YakubovichV. A. (1994) “On M. G. Krein’s work in the theory of linear periodic Hamiltonian systems”, Ukrains’kyi Matematychnyi Zhurnal, 46(1-2), pp. 128–144. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5774 (Accessed: 1September2024).