Positive periodic solutions to predator-prey systems with infinite delay (Q1976594)

Conditions for the existence of positive periodic solutions to a nonautonomous non-convolution predator-prey system with infinite delay \[ \begin{aligned} x'(t) &= x(t)[a(t)-b(t)x(t)-c(t)y(t)],\\ y'(t) &= y(t)[-d(t)+\int_{-\infty}^{t} K(s,t,x(s),x(t)) ds], \end{aligned} \] under certain assumptions on the functions \(K,a,b,c,d\) are given.