@incollection{Watanabe:1962,
	key = "Watanabe 1962",
	author = "S. Watanabe",
	title = "Periodicity of {Post}'s normal process of tag",
	booktitle = "Proceedings of the Symposium on Mathematical
Theory of Automata",
	publisher = "Polytechnic Press",
	year = 1962,
	pages = "83-99"}

@book{Minsky:1967,
	key = "Minsky 1967",
	author = "M. Minsky",
	title = "Computation:  Finite and Infinite Machines",
	publisher = "Prentice-Hall",
	year = 1967,
	comment = "checked; Section 14.6"}

@article{Cocke&Minsky:1964,
	key = "Cocke and Minsky 1964",
	author = "Cocke, J. and Minsky, M.",
	title = "Universality of tag systems with $P = 2$",
	journal = JACM,
	volume = 11,
	year = 1964,
	pages = "15-20",
	comment = "checked"}

@article{Soil:1977,
	key = "Soil 1977",
	author = "Soil, A.",
	title = "Remarks on uniform tag sequences",
	journal = ASAU,
	volume = 23,
	year = 1977,
	pages = "415-418"}

@article{Pansiot:1983a,
	key = "Pansiot 1983",
	author = "Pansiot, J.-J.",
	title = "{Hi\'erarchie} et fermeture de certaines 
classes de {tag-syst\`emes}",
	journal = AI,
	volume = 20,
	year = "{\noopsort{1983a}}1983",
	pages = "179-196"}

@article{Cobham:1972,
	key = "Cobham 1972",
        author = "Cobham, A.",
        title = "Uniform tag sequences",
        journal = MST,
        volume = 6,
        year = 1972,
        pages = "164-192"}

@inproceedings{Cobham:1968b,
	key = "Cobham 1968b",
	author = "A. Cobham",
	title = "On the {Hartmanis-Stearns} problem for a class of
tag machines",
	year = "{\noopsort{1968b}}1968",
	booktitle = "IEEE Conference Record of 1968 Ninth Annual
Symposium on Switching and Automata Theory",
	pages = "51-60",
	note = "Also appeared as IBM Research Technical Report
RC-2178, August 23 1968"}

@incollection{Post:1965,
	key = "Post 1965",
	author = "E. Post",
	title = "Absolutely unsolvable problems and relatively
undecidable propositions:  account of an anticipation",
	booktitle = "The Undecidable",
	editor = "M. Davis",
	year = 1965,
	publisher = "Raven Press",
	pages = "338-433"}