We consider various collections of functions from the Baire space X into itself naturally arising in (effective) descriptive set theory and general topology, including computable (equivalently, recursive) functions, contraction mappings, and functions which are nonexpansive or Lipschitz with respect to suitable complete ultrametrics on X (compatible with its standard topology). We analyze the degree-structures induced by such sets of functions when used as reducibility notions between subsets of X, and we show that the resulting hierarchies of degrees are much more complicated than the classical Wadge hierarchy; in particular, they always contain large infinite antichains, and in most cases also infinite descending chains.

Bad Wadge-like reducibilities on the Baire space

MOTTO ROS, Luca
2014-01-01

Abstract

We consider various collections of functions from the Baire space X into itself naturally arising in (effective) descriptive set theory and general topology, including computable (equivalently, recursive) functions, contraction mappings, and functions which are nonexpansive or Lipschitz with respect to suitable complete ultrametrics on X (compatible with its standard topology). We analyze the degree-structures induced by such sets of functions when used as reducibility notions between subsets of X, and we show that the resulting hierarchies of degrees are much more complicated than the classical Wadge hierarchy; in particular, they always contain large infinite antichains, and in most cases also infinite descending chains.
2014
224
1
67
95
http://arxiv.org/pdf/1212.3005v2
Wadge reducibility; Lipschitz reducibility; Computable functions; Recursive function; Contraction mapping; Nonexpansive function; Lipschitz functions; (Ultra)metric Polish space
MOTTO ROS L
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/148781
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