@article{Lagarias1985,
  author    = {{Jeffrey C. Lagarias}},
  title     = {{The $3x  +  1$ problem and its generalizations}},
  journal   = {{Amer. Math. Monthly}},
  year      = {{1985}},
  volume    = {{92}},
  pages     = {{3--23}},
  note      = {{MR 86i:11043}},
}