@article{Gao1993,
  author    = {{Guo-Gang Gao}},
  title     = {{On consecutive numbers of the same height in the Collatz problem}},
  journal   = {{Discrete Math.}},
  year      = {{1993}},
  volume    = {{112}},
  pages     = {{261--267}},
  note      = {{MR 94i:11018}},
}