@article{Barmpalias2004ApproximationRepresentationsFor2,
  year      = 2004,
  publisher = {Springer},
  volume    = {43},
  number    = {8},
  pages     = {947--964},
  author    = {G. Barmpalias},
  title     = {Approximation Representations for {$\Delta_2$} Reals},
  journal   = {Arch. Math. Logic},
}