KhusainovD. Y., and SheveloV. N. “Stability of Differential Systems With Rational Right-Hand Sides”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 47, no. 9, Sept. 1995, pp. 1295–1299, https://umj.imath.kiev.ua/index.php/umj/article/view/5530.