IGNATYEV A. On the existence of a periodic solution of the Liénard system. Stud. Univ. Babeş-Bolyai Math. [Internet]. 2021 Mar. 30 [cited 2025 Feb. 5];66(1):47-53. Available from: https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/1239