@inproceedings{DLT-1999-KvetonK,
	author        = "Pavel Kveton and Václav Koubek",
	booktitle     = "{Proceedings of the Fourth International Conference on Developments in Language Theory, Foundations, Applications, and Perspectives}",
	isbn          = "981-02-4380-4",
	pages         = "81--102",
	publisher     = "{World Scientific}",
	title         = "{Functions preserving classes of languages}",
	year          = 1999,
}