Computability in Europe 2006
Logical Approaches to Computational Barriers

## Regular Talk: Describing the Wadge Hierarchy for the Alternation Free Fragment of $\mu$-Calculus (I): The Levels Below $\omega_{1}$

 Author(s): Jacques Duparc and Alessandro Facchini Slot: Array, 12:20-12:40, col. 4

### Abstract

The height of the Wadge Hierarchy for the Alternation Free
Fragment of $\mu$-calculus is known to be at least $\epsilon_{0}$.  It was
conjectured that the height is exactly $\epsilon_{0}$. We make a first step
towards the proof of this conjecture by showing that there is no
$\Delta^\mu_{2}$ definable set in between the levels $\omega^\omega$ and
$\omega_{1}$ of the Wadge Hierarchy of Borel Sets.


 websites: Arnold Beckmann 2008-05-18