“…In this paper, based on some recent work on positivity of solotions [6,7,15] and by virtue of some properties of a Green's function, some recent results such as those obtained in [3,5,11,14,18] and a Krasnoselskii fixed point theorem, we investigate the existence and positivity of periodic solutions for the following class of second order iterative differential equations: [2] (t), ..., x [n] (t) +…”