Discrete and Backlund (!) transformations of SDYM system
  Symmetry of SDYM equations for "physically restricted solution" with hermitian group element $G=G^H$ in representation of Yang is described. Such transformation $D^B$ pass some PRS to the new one of the same kind. Transformation contain $2N_G$ arbirtrary functions of two independent arguments, where $N_G$ dimension of the gauge semi-simple algebra. These functions may be considered as additional parameters typical for Backlund aproach and by this reason we use term Backlund for this transformation. 
A. N. Leznov