Existence of positive periodic solutions for neutral functional differential equations

Applying a fixed point theorem of strict-set-contraction, some new criteria are established for the existence of positive periodic solutions of the following neutral functional differential equation: x′(t)=x(t)[a(t)−F(t,x(t),x(t−σ1(t)),…,x(t−σn(t)),x′(t−τ1(t)),…,x′(t−τm(t)))].x′(t)=x(t)[a(t)−F(t,x(t),x(t−σ1(t)),…,x(t−σn(t)),x′(t−τ1(t)),…,x′(t−τm(t)))].