A. Gasull, R. Prohens, and J. Torregrosa, Limit cycles for rigid cubic systems, Journal of Mathematical Analysis and Applications, vol.303, issue.2, pp.391-404, 2005.
DOI : 10.1016/j.jmaa.2004.07.030

URL : https://doi.org/10.1016/j.jmaa.2004.07.030

N. G. Lloyd, A Note on the Number of Limit Cycles in Certain Two-Dimensional Systems, Journal of the London Mathematical Society, vol.2, issue.2, pp.20-277, 1979.
DOI : 10.1112/jlms/s2-20.2.277

R. E. Mickens, Oscillations in Planar Dynamic Systems, World Scientific, vol.37, 1996.
DOI : 10.1142/2778

A. Stokes, On the approximation of nonlinear oscillations, Journal of Differential Equations, vol.12, issue.3, pp.535-558, 1972.
DOI : 10.1016/0022-0396(72)90024-1

M. Urabe, Galerkin's procedure for nonlinear periodic systems, Archive for Rational Mechanics and Analysis, vol.20, issue.2, pp.120-152, 1965.
DOI : 10.1007/BF00284614

M. Urabe and A. Reiter, Numerical computation of nonlinear forced oscillations by Galerkin's procedure, Journal of Mathematical Analysis and Applications, vol.14, issue.1, pp.107-140, 1966.
DOI : 10.1016/0022-247X(66)90066-7

URL : https://doi.org/10.1016/0022-247x(66)90066-7