Vereikina, M. B., and O. M. Sharkovsky. 1997. “Tracing of Pseudotrajectories of Dynamical Systems and Stability of Prolongations of Orbits”. Ukrains’kyi Matematychnyi Zhurnal 49 (8), 1016–1024. https://umj.imath.kiev.ua/index.php/umj/article/view/5096.