@article{Hin09Bir,
  title = "{Functional Pearl:} {The} {Bird} Tree",
  author = "Hinze, Ralf",
  year = "2009",
  journal = "JFP",
  number = "5",
  pages = "491–508",
  volume = "19",
  doi = "10.1017/S0956796809990116",
}