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 28 December 2025]. DOI 10.12775/TMNA.2021.063.