@inproceedings{ICALP-v2-2006-LohreyS,
	author        = "Markus Lohrey and Géraud Sénizergues",
	booktitle     = "{Proceedings of the 33rd International Colloquium on Automata, Languages and Programming, Part II}",
	doi           = "10.1007/11787006_43",
	isbn          = "3-540-35907-9",
	pages         = "504--515",
	publisher     = "{Springer International Publishing}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{Theories of HNN-Extensions and Amalgamated Products}",
	volume        = 4052,
	year          = 2006,
}