@article{Gronau:1994,
  author  = "D. Gronau and J. Matkowski",
  title   = "Geometrically convex solutions of certain difference equations and generalized Bohr-Mollerup type theorems",
  journal = "Results in Mathematics. Resultate der Mathematik",
  volume  = "Vol. 26",
  number  = "no 3-4",
  pages   = "290--297",
  year    = "1994",
}