Mitropolsky , Yu. O., et al. “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.