@inproceedings{STOC-1970-Cudia,
	author        = "Dennis F. Cudia",
	booktitle     = "{Proceedings of the Second Annual ACM Symposium on Theory of Computing}",
	doi           = "10.1145/800161.805144",
	pages         = "10--21",
	publisher     = "{ACM}",
	title         = "{The Degree Hierarchy of Undecidable Problems of Formal Grammars}",
	year          = 1970,
}