1. Alexander, J.C., & J.A. Yorke, Global Bifurcation of Periodic Orbits (to appear).
2. Brushinskaya, N.N., Qualitative integration of a system of n differential equations in a region containing a singular point and a limit cycle. Dokl. Akad. Nauk. SSSR 139, 9–12 (1961).
3. Chafee, N., The bifurcation of one or more closed orbits from an equilibrium point of an autonomous differential system. J. Differential Equations 4, 661–679 (1968).
4. Coppel, W.A., Stability and Asymptotic Behavior of Differential Equations. Boston: D. C. Heath 1965.
5. Dieudonné, J., Foundations of Modern Analysis. New York: Academic Press 1969.