1. Dumortier, F., Llibre, J., Artés, J.C.: Qualitative theory of planar differential systems. UniversiText, Springer-Verlag, New York (2006)
2. Krantz, S.G., Parks, H.R.: The Implicit Function Theorem: History, Theory, and Applications. Modern Birkhäuser Classics. Springer, New York (2013)
3. Liénard, A.: Étude des oscillations entretenues. Rev. Gén. Électr. 23, 946–954 (1928)
4. Llibre, J., Valls, C.: Non-existence and uniqueness of limit cycles in a class of generalized Liénard equations. Bol. Soc. Mat. Mex. (3) 28(2), 12 (2022). (Paper No. 41)
5. Newton, I.: Letter from Newton to Oldenburg dated October 24, 1696. In: Turnbull, H.W. (ed.) The Correspondence of Isaac Newton, pp. 110–161. Cambridge University Press, UK (1960)