PageHeader : Funkcialaj Ekvacioj, 28 (1985), 39-46 Title : On the Periodic Problem for the Equation Title : $x^{\prime\prime}(t)+g(x(t))=f(t)$ AuthorInfo : By AuthorInfo : Stepan TERSIAN AuthorInfo : (Technical University, Rousse, Bulgaria) section : 0. Introduction section : 1. Notations and main result section : 2. Proof of the main result section : References