Subharmonic solutions of systems of difference equations with periodic perturbations Part I: Existence

We consider the existence of subharmonic solutions of systems of difference equations with periodic perturbations. The theory of coincidence degree, coupled with some detailed a priori estimates, is applied to show that the perturbed system admits subharmonic solutions near a hyperbolic periodic orbit of the unperturbed system if the perturbation is sufficiently small.  2002 Elsevier Science (USA). All rights reserved