Translation and homothetical surfaces in Euclidean space with constant   curvature
  We study surfaces in Euclidean space constructed by the sum of two curves or that are graphs of the product of two functions. We consider the problem to determine all these surfaces with constant Gauss curvature. We extend the results to non degenerate surfaces in Lorentz-Minkowski space. 
Rafael L\'opez and Marilena Moruz
math.DG