Zero-curvature condition in two dimensions. Relativistic particle models and finite \W-transformations

In the last few years a lot of attention has been devoted to the study of W-algebras[1]. For recent update reviews see [2], [3] where extensive lists of references can befound.An interesting way to construct classical W-algebras isbythe zero-curvature method[4], [5], [6],[7] [8]. If one constraints an A