@inproceedings{STOC-1969-Johansen,
	author        = "Peter Johansen",
	booktitle     = "{Proceedings of the First Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800169.805426",
	pages         = "113--128",
	publisher     = "{ACM}",
	title         = "{Free Groups and Regular Expressions}",
	year          = 1969,
}