@inproceedings{ICALP-1987-Karhumaki,
	author        = "Juhani Karhumäki",
	booktitle     = "{Proceedings of the 14th International Colloquium on Automata, Languages and Programming}",
	doi           = "10.1007/3-540-18088-5_12",
	isbn          = "3-540-18088-5",
	pages         = "136--162",
	publisher     = "{Springer-Verlag}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{On Recent Trends in Formal Language Theory}",
	volume        = 267,
	year          = 1987,
}