@article{BirdPaterson99:Generalised,
  title = "Generalised Folds for Nested Datatypes",
  author = "Richard Bird and Ross Paterson",
  year = "1999",
  journal = "Formal Aspects of Computing",
  pages = "200--222",
  url = "http://www.cs.ox.ac.uk/people/richard.bird/online/BirdPaterson99Generalised.pdf",
  volume = "11",
}