@inproceedings{PPDP-2005-CastagnaF,
	author        = "Giuseppe Castagna and Alain Frisch",
	booktitle     = "{Proceedings of the Seventh International Conference on Principles and Practice of Declarative Programming}",
	doi           = "10.1145/1069774.1069793",
	isbn          = "1-59593-090-6",
	pages         = "198--199",
	publisher     = "{ACM}",
	title         = "{A gentle introduction to semantic subtyping}",
	year          = 2005,
}