@article{Yang1998,
  author    = {{Yang, Zhao Hua}},
  title     = {{An equivalent set for the $3x+1$ conjecture}},
  journal   = {{J. South China Normal Univ. Natur. Sci. Ed. 
[ Hua nan shi fan da xue xue bao. Zi ran ke xue ban]}},
  year      = {{1998}},
  pages     = {{66--68}},
  note      = {{MR 2001f:11040}},
}