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”, Ukr. Mat. Zhurn., vol. 44, no. 1, pp. 46-66, Feb. 1992.