@article{Garner1985,
  author    = {{Lynn E. Garner}},
  title     = {{On heights in the Collatz $3n  +  1$ problem}},
  journal   = {{Discrete Math.}},
  year      = {{1985}},
  volume    = {{55}},
  pages     = {{57--64}},
  note      = {{MR 86j:11005}},
}