N^N^N does not satisfy Normann's condition
Logic
2010-10-13 v1 Logic in Computer Science
Abstract
We prove that the Kleene-Kreisel space N^N^N does not satisfy Normann's condition. A topological space is said to fulfil Normann's condition, if every functionally closed subset of is an intersection of clopen sets. The investigation of this property is motivated by its strong relationship to a problem in Computable Analysis. D. Normann has proved that in order to establish non-coincidence of the extensional hierarchy and the intensional hierarchy of functionals over the reals it is enough to show that N^N^N fails the above condition.
Cite
@article{arxiv.1010.2396,
title = {N^N^N does not satisfy Normann's condition},
author = {Matthias Schroeder},
journal= {arXiv preprint arXiv:1010.2396},
year = {2010}
}
Comments
10 pages