@inproceedings{STOC-1973-Eilenberg,
	author        = "Samuel Eilenberg",
	booktitle     = "{Proceedings of the Fifth Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800125.804057",
	pages         = "266--267",
	publisher     = "{ACM}",
	title         = "{Classes of Semigroups and Classes of Sets}",
	year          = 1973,
}