00425nam a2200133 a 450000500170000002000180001708200160003510000060005111000450005724500570010226000480015930000250020749000590023220251203110725.0  a9780521596992  a515.35bSYM  d_  aClarkson, Peter A. and Nijhoff, Frank W.  aSymmetries and Integrability of Difference Equations  aCambridgebCambridge University Pressc1999  axvi,424p.c28 cm. PB  aLondon Mathematical Society Lecture Note Seriesdv.255