Nomirovs’kiiD. A. “Solvability and Trajectory-Final Controllability of Pseudohyperbolic Systems”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 57, no. 3, Mar. 2005, pp. 366–376, https://umj.imath.kiev.ua/index.php/umj/article/view/3604.