Group Theoretical Symmetries and Generalized Baecklund Transformations   for Integrable Systems
  We present a notion of symmetry for 1+1-dimensional integrable systems which is consistent with their group theoretic description and reproduces in special cases the known Baecklund transformation for the generalized Korteweg-deVries hierarchies. We also apply it to the relativistic invariance of the Leznov-Saveliev systems. 
G. Haak