@article{Barmpalias2009KTrivialDegrees,
  year      = 2009,
  publisher = {AMS},
  volume    = {137},
  number    = {06},
  pages     = {2099--2109},
  author    = {G. Barmpalias and R. Downey and N. Greenberg},
  title     = {{$K$}-trivial degrees and the jump-traceability hierarchy},
  journal   = {Proc. Amer. Math. Soc.},
}