  In this paper we propose a process of lagrangian reduction and reconstruction
for nonholonomic discrete mechanical systems where the action of a continuous
symmetry group makes the configuration space a principal bundle. The result of
the reduction process is a discrete dynamical system that we call the discrete
reduced system. We illustrate the techniques by analyzing two types of discrete
symmetric systems where it is possible to go further and obtain (forced)
discrete mechanical systems that determine the dynamics of the discrete reduced
system.
