On systems of rational difference equations and periodic tetrachotomies

We study the following system of two rational difference equations x_n=({\beta}k x(n-k)+{\gamma}k y(n-k))/(A+\Sigma_(j=1)^l[B_j x_(n-j) ]+\Sigma_(j=1)^l[C_j y_(n-j) ]), n \in N, y_n=({\delta}k x(n-k)+\in_k y_(n-k))/(q+\Sigma_(j=1)^l[D_j x_(n-j) ]+\Sigma_(j=1)^l[E_j y_(n-j) ]), n\in N, with nonnegative parameters and nonnegative initial conditions. We assume that B_j=C_j=D_j=E_j=0 for j=k, 2k, 3k, …and establish the existence of periodic tetrachotomy behavior which depends on a 2X2 matrix with entries {\beta}_k, {\gamma}_k, {\delta}_k, and \in_k.