@article{Stachowiak:2006,
  author  = "T. Stachowiak and M. Szydłowski and A. Maciejewski",
  title   = "Nonitegrability of density perturbations in the Friedmann-Robertson-Walker universe",
  journal = "Journal of Mathematical Physics",
  volume  = "Vol. 47",
  pages   = "032502-1--032502-11",
  year    = "2006",
}