[1] C. Chicone, Ordinary differential equations with applications, Second edition, Texts in Applied Mathematics, 34, Springer, New York, 2006.
[2] J. Gruendler, Homoclinic solutions for autonomous ordinary differential equations with nonautonomous perturbations, J. Differential Equations, 122 no. 1 (1995) 1–26.
[3] M. Han, Z. Wang and H. Zang, Limit cycles by Hopf and homoclinic bifurcations for near-Hamiltonian systems, Chinese J. Contemp. Math, 28 no. 4 (2007) 423–434.
[4] M. Han, J. Yang, A. Tarta and Y. Gao, Limit cycles near homoclinic and heteroclinic loops, J. Dynam. Differential Equations, 20 no. 4 (2008) 923–944.
[5] R. Johnson, X. B. Pan and Y. F. Yi, The Melnikov method and elliptic equations with critical exponent, Indiana Univ. Math. J., 43 (1994) 1045–1077
[6] P. Kuku¡cka, Melnikov method for discontinuous planar systems, Nonlin. Anal., 66 (2007) 2698–2719.
[7] L. Perko, Differential equations and dynamical systems, Springer-Verlag, New York, 2012.
[8] J. Yang and M. Han, Limit cycle bifurcations of some Liénard systems with a cuspidal loop and a homoclinic loop, Chaos Solitons Fractals, 44 (2011) 269–289.
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