Mitropolsky Y. O., Antonishin I. O., Prikarpatsky A. K., and Samoilenko V. G. “Simplex Analysis of Dynamical Systems With a Perturbation. New Criteria of Stabilization of a Homoclinic Separatrix and Its Use”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 44, no. 1, Feb. 1992, pp. 46-66, https://umj.imath.kiev.ua/index.php/umj/article/view/2319.