@article{Z09:ipl,
  title = "Structural properties of oracle classes",
  author = "Stanislav \v{Z}ivn\'y",
  year = "2009",
  journal = "Information Processing Letters",
  number = "19",
  pages = "1131--1135",
  url = "http://zivny.cz/publications/z09ipl-preprint.pdf",
  volume = "109",
  doi = "10.1016/j.ipl.2009.07.009",
}