@inproceedings{STOC-1972-Cook,
	author        = "Stephen A. Cook",
	booktitle     = "{Proceedings of the Fourth Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800152.804913",
	pages         = "187--192",
	publisher     = "{ACM}",
	title         = "{A Hierarchy for Nondeterministic Time Complexity}",
	year          = 1972,
}