J. P. La Salle has developed in [20] a stability theory for systems of
difference equations (see also [8]) which we introduce in the first
chapter within the framework of metric spaces. The stability theory for
such systems can also be found in [13] in a slightly modified form. We
start with autonomous systems in the first section of chapter 1. After
theoretical preparations we examine the localization of limit sets with
the aid of Lyapunov Functions. Applying these Lyapunov Functions we can
develop a stability theory for autonomous systems. If we linearize a
non-linear system at a fixed point we are able to develop a stability
theory for fixed points which makes use of the Frechet derivative at the
fixed point. The next subsection deals with general linear systems for
which we intro- duce a new concept of stability and asymptotic stability
that we adopt from [18]. Applications to various fields illustrate
these results. We start with the classical predator-prey-model as being
developed and investigated by Volterra which is based on a 2 x 2-system
of first order differential equations for the densities of the prey and
predator population, respectively. This model has also been investigated
in [13] with respect to stability of its equilibrium via a Lyapunov
function. Here we consider the discrete version of the model.