@article{llibre_messias_2007,  title={Large amplitude oscillations for a class of symmetric polynomial differential systems in R³},  volume={79},  ISSN={0001-3765},  url={https://doi.org/10.1590/S0001-37652007000400001},  DOI={10.1590/S0001-37652007000400001},  number={4},  journal={Anais da Academia Brasileira de Ciências},  publisher={Academia Brasileira de Ciências},  author={Llibre, Jaume and Messias, Marcelo},  year={2007},  month={Dec},  pages={563–575} }