Ma, Tiantian. “Periodic Solutions of a Kind of Liénard Equations With Two Deviating Arguments”. Topological Methods in Nonlinear Analysis 44, no. 2 (April 12, 2016): 337–348. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2014.049.