Positive periodic solutions for a neutral delay Lotka-Volterra system

Applying a fixed point theorem of strict-set-contraction, some new criteria are established for the existence of positive periodic solutions for a class of neutral delay Lotka-Volterra systems: xi′(t)=xi(t)[ri(t)−∑j=1naij(t)xj(t)−∑j=1nbij(t)xj(t−τij(t))−∑j=1ncij(t)xj′(t−σij(t))],i=1,2,…,n. Compared to known results, our main generalization is that delays of the derivatives are not assumed to be constants, and our results are more easily verifiable.