  In this paper we discuss a universal integrable model, given by a sum of two
Wess-Zumino-Witten-Novikov (WZWN) actions, corresponding to two different
orbits of the coadjoint action of a loop group on its dual, and the
Polyakov-Weigmann cocycle describing their interactions. This is an effective
action for free fermions on a torus with nontrivial boundary conditions. It is
universal in the sense that all other known integrable models can be derived as
reductions of this model. Hence our motivation is to present an unified
description of different integrable models. We present a proof of this
universal action from the action of the trivial dynamical system on the
cotangent bundles of the loop group. We also present some examples of
reductions.
