@article{CIAA-J-2004-BordihnHK05,
	author        = "Henning Bordihn and Markus Holzer and Martin Kutrib",
	doi           = "10.1142/S0129054105003078",
	journal       = "{International Journal of Foundations of Computer Science}",
	number        = 3,
	pages         = "423--440",
	publisher     = "{World Scientific}",
	title         = "{Unsolvability levels of operation problems for subclasses of context-free languages}",
	volume        = 16,
	year          = 2005,
}