MOTA, Marcos Coutinho, REZENDE, Alex Carlucci, SCHLOMIUK, Dana and VULPE, Nicolae. Geometric analysis of quadratic differential systems with invariant ellipses. Topological Methods in Nonlinear Analysis. Online. 10 April 2022. Vol. 59, no. 2A, pp. 623 - 685. [Accessed 22 July 2024]. DOI 10.12775/TMNA.2021.063.