Mitropolsky Y. O.; Antonishin I. O.; Prikarpatsky A. K.; 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, v. 44, n. 1, p. 46-66, 4 Feb. 1992.