Existence of periodic solutions for Liénard equations with finite delay (Q1373821)

This paper deals with the existence of periodic solutions of the Liénard equation with finite delay \[ \ddot x(t)+ f(x(t)) \dot x(t)+g(x(t-r))=0 \] under some assumptions such that the results can be applied to the sunflower equation \[ \ddot x(t) +{\textstyle(\frac ar)\dot x(t)+(\frac br)}\sin x(t-r)=0, \] which is related to the work of the authors [ Chin. Sci. Bull. 40, No. 12, 981-983 (1995; Zbl 0831.34078)] and \textit{A. S. Somolinos} [Q. Appl. Math. 35, 465-478 (1978; Zbl 0385.34017)].