@article{LagariasWeiss1992,
  author    = {{Jeffrey C. Lagarias and Alan Weiss}},
  title     = {{The $3x  +  1$ Problem: Two Stochastic Models}},
  journal   = {{Annals of Applied Probability}},
  year      = {{1992}},
  volume    = {{2}},
  pages     = {{229--261}},
  note      = {{MR 92k:60159}},
}