@article{Matkowski:2008,
  author  = "J. Matkowski",
  title   = "Iteration groups, commuting functions and simultaneous systems of linear functional equations",
  journal = "Opuscula Mathematica",
  volume  = "Vol. 28",
  number  = "no 4",
  pages   = "531--540",
  year    = "2008",
}