Periodic solutions to a kind of neutral functional differential equation in the critical case

In this paper, we consider a kind of neutral functional differential equation as follows: <fen><cp type="lpar" STYLE="S">x(t)−cx(t−τ)<cp type="rpar" STYLE="S"></fen>′=g<fen><cp type="lpar" STYLE="S">t,x<fen><cp type="lpar" STYLE="S">t−μ(t)<cp type="rpar" STYLE="S"></fen><cp type="rpar" STYLE="S"></fen>+e(t) in the critical case <f>&z.sfnc;c&z.sfnc;=1</f>. By employing the topological degree theory and some analysis techniques, we obtain some new results on the existence of periodic solutions. [Copyright &y& Elsevier]