1. Theory and Application of Hopf Bifurcation;Hassard,1981
2. Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields. Corrected 6th Printing;Guckenheimer,2002
3. Elements of Applied Bifurcation Theory;Kuznetsov,1995
4. Normal forms for certain singularities of vectorfields;Takens;Ann. Inst. Fourier,1973
5. Hypernormal forms for equilibria of vector fields. Codimension one linear degeneracies;Algaba;Rocky Mountain J. Math.,1999