“…For example, the mathematical modeling of a variety of physical processes gives rise to periodic solutions. For this reason, existence of periodic solutions to nonlinear differential inclusions has been extensively investigated by many authors in the last decades (see [9,10,11,12,13,14,15,16,17,18]). Recently, periodic solution for (2) associated with monotone operators has received some attention (see [8,9,10,15,19,20,21]).…”