@article{Li2003,
  author    = {{Li, Xiao Chun}},
  title     = {{Contractible iteration for the $3n+1$ conjecture}},
  journal   = {{J. Huazhong Univ. Sci. Technol. Nat. Sci.}},
  year      = {{2003}},
  volume    = {{31}},
  number    = {{7}},
  pages     = {{115--116}},
  note      = {{MR 2025640}},
}