@article{Barmpalias2003TransfiniteHierarchyReals,
  year      = 2003,
  publisher = {Wiley-Blackwell},
  volume    = {49},
  number    = {2},
  pages     = {163--172},
  author    = {G. Barmpalias},
  title     = {A transfinite hierarchy of reals},
  journal   = {{MLQ}},
}