@article{Cadogan2003,
  author    = {{Charles C. Cadogan}},
  title     = {{Trajectories in the $3x+1$ problem}},
  journal   = {{J. of Combinatorial Mathematics and Combinatorial Computing}},
  year      = {{2003}},
  volume    = {{44}},
  pages     = {{177--187}},
  note      = {{MR 2004a:11017}},
}