[1] Dan Liu, Fengjie Geng, Deming Zhu,
     Degenerate bifurcations of nontwisted heterodimensional cycles with codimension 3,
     Nonlinear Analysis: Theory, Methods & Applications, 2008, 68(9): 2813-2827. 

[2] Fengjie Geng, Dan Liu, Deming Zhu,
     Bifurcations of generic heteroclinic loop accompanied by transcritical bifurcation,
     International Journal of Bifurcation and Chaos, 2008, 18(4): 1069-1083. 

[3] Weipeng Zhang, Deming Zhu, Dan Liu,
     Codimension 3 nontwisted double homoclinic loops bifurcations with resonant eigenvalues,
     Journal of Dynamics and Differential Equations, 2008, 20(4): 893-908.

[4] Dan Liu, Shigui Ruan, Deming Zhu,
     Bifurcation analysis in models of tumor and immune system interactions,
     Discrete and Continuous Dynamical System Series B, 2009, 12(1): 151-168. 

[5] Dan Liu, Shigui Ruan, Deming Zhu,
     Nongeneric bifurcations near heterodimensional cycles with inclination flip in R4,
     Discrete and Continuous Dynamical System Series S, 2011, 4(6): 1011-1032.

[6] Dan Liu, Shigui Ruan, Deming Zhu,
     Stable periodic oscillations in a two-stage cancer model of tumor and immune system interactions,
     Mathematical Biosciences and Engineering, 2012, 9(2): 347-368. 

[7] Dan Liu, Maoan Han, Weipeng Zhang, 
     Bifurcations of 2-2-1 heterodimensional cycles under transversality condition,
     International Journal of Bifurcation and Chaos, 2012,  22(8): **-**.   

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