Integrability, Centre, Period function, Quasi-homogeneous polynomial, Center-focus problem, Vector field.
 A. Algaba, E. Freire, E. Gamero, and C. Garca, "Monodromy, centre-focus and integrability problems for quasi-homogeneous polynomial systems," Nonlinear Analysis, vol. 72, pp. 1726-1736, 2010. View at Google Scholar | View at Publisher
 A. Algaba, N. Fuentes, and C. Garca, "Centre of quasi-homogeneous polynomial planar systems," Nonlinear Analysis: Real World Applications, vol. 13, pp. 419-431, 2012. View at Google Scholar | View at Publisher
 M. J. Alvarez, A. Gasull, and R. Prohens, "Global behavior of the period function of the sum of two quasi-homogeneous vecto fields," Journal of Mathematical Analysis and Applications, vol. 449, pp. 1553-1569, 2017. View at Google Scholar | View at Publisher
 J. Chavarriga and M. Sabatini, "A survey of isochronous centres," Qualitative Theory of Dynamical Systems, vol. 1, pp. 1-70, 1999. View at Google Scholar
 J. Gine and J. Llibre, "On the centre conditions for analytic monodromic degenerate singularities," International Journal of Bifurcation and Chaos Applied Sciences and Engineering, vol. 22, p. 1250303, 2012. View at Google Scholar | View at Publisher
 Y. Xiong, M. Han, and Y. Wang, "Centre problems and limit cycle bifurcations in a class of quasi-homogeneous system," International Journal of Bifurcation and Chaos, vol. 25, p. 1550135, 2015. View at Google Scholar | View at Publisher