VereikinaM. B., and SharkovskyO. M. “Tracing of Pseudotrajectories of Dynamical Systems and Stability of Prolongations of Orbits”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 49, no. 8, Aug. 1997, pp. 1016–1024, https://umj.imath.kiev.ua/index.php/umj/article/view/5096.