Battelli, F., and K. J. Palmer. “Connections to Fixed Points and Sil’nikov Saddle-Focus Homoclinic Orbits in Singularly Perturbed Systems”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 1 (January 25, 2008): 28–55. Accessed March 29, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3135.