@article{PatersonRA:gfold,
	title = "Generalised Folds for Nested Datatypes",
	author = "Richard Bird and Ross Paterson",
	journal = "Formal Aspects of Computing",
	volume = 11,
	number = 2,
	pages = "200-222",
	url = "http://www.soi.city.ac.uk/~ross/papers/gfold.html",
	year = 1999
}