Bingwen Liu Lihong Huang Existence and uniqueness of periodic solutions for a kind of Liénard equation with a deviating argument. 56-62 2008 21 Appl. Math. Lett. 1 http://dx.doi.org/10.1016/j.aml.2006.07.018 db/journals/appml/appml21.html#LiuH08