Zakharov-Shabat system and hyperbolic pseudoanalytic function theory
  In [1] a hyperbolic analogue of pseudoanalytic function theory was developed. In the present contribution we show that one of the central objects of the inverse problem method the Zakharov-Shabat system is closely related to a hyperbolic Vekua equation for which among other results a generating sequence and hence a complete system of formal powers can be constructed explicitly. 
Viktor G. Kravchenko, Vladislav V. Kravchenko and S\'ebastien Tremblay