Periodic solutions for a kind of Liénard equation with a deviating argument

In this paper, the Liénard equation with a deviating argument x″(t)+f1(t,x(t))x′(t)+f2(x(t))(x′(t))2+g(t,x(t−τ(t)))=p(t) is studied. By applying the coincidence degree theory, we obtain some new results on the existence and uniqueness of T-periodic solutions to this equation. Our results improve and extend some existing ones in the literature.