@article{Keller1999,
  author    = {{Timothy P. Keller}},
  title     = {{Finite cycles of certain periodically linear functions}},
  journal   = {{Missouri J. Math. Sci.}},
  year      = {{1999}},
  volume    = {{11}},
  number    = {{3}},
  pages     = {{152--157}},
  note      = {{MR 1717767}},
}