Generalized hyperbolic Ernst equations for an Einstein-Maxwell-Weyl   field
  A new family of nonlinear partial differential equations is presented. They represent a generalization of the hyperbolic Ernst equations for an Einstein-Mawxell-Weyl field in general relativity. A B\"acklund transformation for the system of equations under consideration is given, and their direct relation to the complete Boussinesq hierarchy of soliton equations is illustrated. 
Anastasios Tongas and Frank Nijhoff