Backlund Transformations for Darboux Integrable Differential Systems:   Examples and Applications
  In the article arXiv:1108.5443 we established a general group-theoretical approach to the construction of B\"acklund transformations. We then showed how this construction can be applied to construct B\"acklund transformation between equations which are Darboux integrable. Here we give a number of detailed examples and new applications which demonstrate the theory. In particular our final example demonstrates how our group theoretical approach produces all the B\"acklund transformations in arXiv:0707.4408. We also prove, using group methods, a non-existence theorem for B\"acklund transformatons which disagrees with part 2 of Theorem 1 in arXiv:0707.4408. 
Ian M. Anderson, Mark E. Fels
math.DG