@article{ABCS07,
  title = "Post's programme for the {Ershov} hierarchy",
  author = "Bahareh Afshari and George Barmpalias and S. Barry Cooper and Frank Stephan",
  year = "2007",
  journal = "Journal of Logic and Computation",
  number = "6",
  pages = "1025--1040",
  volume = "17",
  doi = "10.1093/logcom/exm032",
}