BattelliF., & PalmerK. J. (2008). Connections to fixed points and Sil’nikov saddle-focus homoclinic orbits in singularly perturbed systems. Ukrains’kyi Matematychnyi Zhurnal, 60(1), 28–55. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/3135