TkachenkoV. I. “On Reducibility of Systems of Linear Differential Equations With Quasiperiodic Skew-Adjoint Matrices”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 54, no. 3, Mar. 2002, pp. 419-24, https://umj.imath.kiev.ua/index.php/umj/article/view/4079.