@inproceedings{STOC-1970-Ullian,
	author        = "Joseph S. Ullian",
	booktitle     = "{Proceedings of the Second Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800161.805169",
	pages         = "226--230",
	publisher     = "{ACM}",
	title         = "{Three Theorems on Abstract Families of Languages}",
	year          = 1970,
}