Lungu, N. “On the Existence of Limit Cycles for an Autonomous System”. Anal. Numér. Théor. Approx. 15, no. 2 (August 1, 1986): 141–144. Accessed May 2, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1986-vol15-no2-art7.