# A Normal Form for Borel Sets

### Details

Serval ID

serval:BIB_AAB777A7CF36

Collection

Publications

Fund

Title

A Normal Form for Borel Sets

Language

english

Notes

extended abstract, not submitted

Abstract

For each Borel set A of reals, or more generally of infinite strings from a countable alphabet, we obtain a ``normal form'' ofA, by finding a Borel setΩ of maximum simplicity, such that A and Ω continuously reduce to each other.Ω only depend on the equivalence class of A modulo inter-reducibility, moreover, the map: A→Ω is defined in a simple way (in ZF+DC). In case of Borel sets of finite rank, we prove the above result essentially by defining simple Borel operations which are homomorphic to ordinal sum, to multiplication by a countable ordinal, and to ordinal exponentiation of base ω1 (under the map which sends every Borel setA of finite rank to its Wadge degree). Extension to transfinite ranks is provided by iterating both ordinal exponentiation and its Borel counterpart. And finally, we show that all these results can be extended to all Borel subsets of Xω when the alphabet X is of any cardinal.

Keywords

K3

Create date

23/01/2008 19:39

Last modification date

03/03/2018 19:25