@article{Hin09Pur,
  title = "{Functional Pearl:} {Purely} Functional 1-2 Brother Trees",
  author = "Hinze, Ralf",
  year = "2009",
  journal = "JFP",
  number = "6",
  pages = "633-644",
  volume = "19",
  doi = "10.1017/S0956796809007333",
}