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JOURNALS // Sibirskii Matematicheskii Zhurnal // Archive

Sibirsk. Mat. Zh., 2008 Volume 49, Number 6, Pages 1351–1360 (Mi smj1923)

This article is cited in 1 paper

On the index sets of $\Sigma$-subsets of the real numbers

A. S. Morozov

Sobolev Institute of Mathematics, Siberian Branch of the Russian Academy of Sciences

Abstract: We compute the levels of complexity in analytical and arithmetical hierarchies for the sets of the $\Sigma$-formulas defining in the hereditarily finite superstructure over the ordered field of the reals the classes of open, closed, clopen, nowhere dense, dense subsets of $\mathbb R^n$, first category subsets in $\mathbb R^n$ as well as the sets of pairs of $\Sigma$-formulas corresponding to the relations of set equality and inclusion which are defined by them. It is also shown that the complexity of the set of the $\Sigma$-formulas defining connected sets is at least $\Pi^1_1$.

Keywords: computability over the reals, sigma-formula, admissible set, index set, hereditarily finite superstructure.

UDC: 510.6+510.5

Received: 04.05.2007


 English version:
Siberian Mathematical Journal, 2008, 49:6, 1078–1084

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© Steklov Math. Inst. of RAS, 2025