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 2 May 2026]. DOI 10.12775/TMNA.2021.063.