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A theorem on hyperhypersimple sets

Published online by Cambridge University Press:  12 March 2014

Donald A. Martin*
Affiliation:
University of Chicago

Extract

Let be the class of recursively enumerable (r.e.) sets with infinite complements. A set M ϵ is maximal if every superset of M which is in is only finitely different from M. In [1] Friedberg shows that maximal sets exist, and it is an easy consequence of this fact that every non-simple set in has a maximal superset. The natural question which arises is whether or not this is also true for every simple set (Ullian [2]). In the present paper this question is answered negatively. However, the main concern of this paper is with demonstrating, and developing a few consequences of, what might be called the “density” of hyperhypersimple sets.

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1964

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References

[1]Friedberg, R. M., Three theorems on recursive enumeration. Journal of Symbolic Logic, vol. 23 (1958), pp. 309316.CrossRefGoogle Scholar
[2]Ullian, J. S., A theorem on maximal sets, Notre Dame Journal of Formal Logic, vol. II (1961), pp. 222223.Google Scholar
[3]Rice, H. G., Recursive and recursively enumerable orders, Transactions of the American Mathematical Society, vol. 83 (1956), pp. 277300.CrossRefGoogle Scholar
[4]Post, E. L., Recursively enumerable sets of positive integers and their decision problems, Bulletin of the American Mathematical Society, vol. 50 (1944), pp. 284316.CrossRefGoogle Scholar