[1] | P. Alsholm, Existence of limit cycles for generalized Liénard equations. J. Math. Anal. Appl., 1992, 171(1), 242-255. |

[2] | L. A. Cherkas, Estimation of the number of limit cycles of autonomous systems. Differ. Uravn., 1977, 171, 779-802,translation in Differ. Equ., 1977, 13, 529-547. |

[3] | M. P. Do Carmo, Differential geometry of curves and surfaces. Translated from the Portuguese. Prentice-Hall, Inc., Englewood Cliffs, N. J., 1976. |

[4] | G. F. D. Duff, Limit-cycles and rotated vector fields. Ann. of Math. 1953, 57, 15-31. |

[5] | F. Dumortier, J. Llibre and J. C. Artés, Qualitative theory of planar differential systems. Universitext. Springer Verlag, Berlin, 2006. |

[6] | J. D. García-Saldaña and A. Gasull, A theoretical basis for the harmonic balance method. J. Differential Equations, 2013, 254(1), 67-80. |

[7] | H. Giacomini and M. Grau, Transversal conics and the existence of limit cycles, J. Math. Anal. Appl. 2015, 428(1), 563-586. |

[8] | H. Giacomini and S. Neukirch, Number of limit cycles of the Liénard equation, Phys. Rev. E, 1997, 56, 3809-3813. |

[9] | H. Giacomini and S. Neukirch, Algebraic approximations to bifurcation curves of limit cycles for the Liénard equation. Phys. Lett. A, 1998, 244(1-3), 53-58. |

[10] | A. Hungria, J. -P. Lessard and J. D. Mireles James, Rigorous numerics for analytic solutions of differential equations:the radii polynomial approach. Math. Comp., 2016, 85, 1427-1459. |

[11] | T. W. Körner, Fourier analysis. Second edition. Cambridge University Press, Cambridge, 1989. |

[12] | J. Llibre and E. Ponce, Three nested limit cycles in discontinuous piecewise linears differential systems with two zones, Dyn. Contin. Discrete Impuls. Syst. Ser. B Appl. Algorithms, 2012, 19, 325-335. |

[13] | K. Odani, Existence of exactly N periodic solutions for Liénard systems. Funkcial. Ekvac., 1996, 39, 217-234. |

[14] | L. M. Perko, Rotated vector fields. J. Differential Equations, 1993, 103, 127-145. |

[15] | L. M. Perko, Differential equations and dynamical systems. Third edition. Texts in Applied Mathematics, 7. Springer-Verlag, New York, 2001. |

[16] | G. S. Rychkov, The maximum number of limit cycles of polynomial Liénard systems of degree five is equal to two. Differential Equations, 1975, 11, 301-302. |

[17] | J. Stoer and R. Bulirsch, Introduction to numerical analysis. Translated from the German by R. Bartels, W. Gautschi and C. Witzgall. Springer-Verlag, New York-Heidelberg, 1980. |

[18] | A. Stokes, On the approximation of nonlinear oscillations, J. Differential Equations, 1972, 12(3), 535-558. |

[19] | B. Sturmfels, Solving Systems of Polynomial Equations, CBMS Reg. Conf. Ser. Math., vol.97, American Mathematical Society, Providence, RI, 2002, Published for the Conference Board of the Mathematical Sciences, Washington, DC. |

[20] | G. P. Tolstov, Fourier series. Second English translation. Translated from the Russian and with a preface by Richard A. Silverman. Dover Publications, Inc., New York, 1976. |

[21] | W. Tucker, Validated numerics. A short introduction to rigorous computations. Princeton University Press, Princeton, NJ, 2011. |

[22] | M. Urabe, Galerkin's procedure for nonlinear periodic systems, Arch. Ration. Mech. Anal., 1965, 20(2), 120-152. |

[23] | Y. Ye, etc, Theory of limit cycles. Translations of Mathematical Monographs, 66. American Mathematical Society, Providence, RI, 1986. |

[24] | P. Zgliczynski, C1 Lohner algorithm. Found. Comput. Math., 2002, 2(4), 429-465. |

[25] | Z. Zhang, etc, Qualitative theory of differential equations. Translations of Mathematical Monographs, 101. American Mathematical Society, Providence, RI, 1992. |