Backlund transformations for the Nizhnik-Novikov-Veselov equation
  The Backlund transformations for the Nizhnik-Novikov-Veselov equation are presented. It is shown that these transformations can be iterated and that the resulting sequence can be described by the Volterra equations. The relationships between the Nizhnik-Novikov-Veselov equation and the Volterra hierarchy are discussed. 
V.E. Vekslerchik