@inproceedings{ICALP-1989-Steffen,
	author        = "Bernhard Steffen",
	booktitle     = "{Proceedings of the 16th International Colloquium on Automata, Languages and Programming}",
	doi           = "10.1007/BFb0035794",
	isbn          = "3-540-51371-X",
	pages         = "723--732",
	publisher     = "{Springer-Verlag}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{Characteristic Formulae}",
	volume        = 372,
	year          = 1989,
}