# Simple set

From Encyclopedia of Mathematics

A recursively-enumerable set of natural numbers (cf. Enumerable set) whose complement is an immune set. Simple sets are intermediate in the sense of so-called -reducibility (cf. Recursive set theory) between solvable sets and creative sets. The latter are the largest among the enumerable sets in the sense of -reducibility. Let be an arbitrary simple set, and let be an arbitrary creative set of natural numbers (e.g. the set of Gödel numbers of theorems of formal arithmetic); then there does not exist a general recursive function reducing to , i.e. such that

Reducibility of to always takes place, but not one solvable set is reducible to .

#### References

[1] | V.A. Uspenskii, "Leçons sur les fonctions calculables" , Hermann (1966) (Translated from Russian) |

[2] | A.I. Mal'tsev, "Algorithms and recursive functions" , Wolters-Noordhoff (1970) (Translated from Russian) |

[3] | H. Rogers jr., "Theory of recursive functions and effective computability" , McGraw-Hill (1967) pp. 164–165 |

**How to Cite This Entry:**

Simple set.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Simple_set&oldid=18731

This article was adapted from an original article by S.N. Artemov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article