A quasi-order on continuous functions

2013 ◽  
Vol 78 (2) ◽  
pp. 633-648 ◽  
Author(s):  
Raphaël Carroy
Keyword(s):  
Polish Space ◽  
Continuous Functions ◽  
Borel Sets ◽  
Borel Functions ◽  
Quasi Order

AbstractWe define a quasi-order on Borel functions from a zero-dimensional Polish space into another that both refines the order induced by the Baire hierarchy of functions and generalises the embeddability order on Borel sets. We study the properties of this quasi-order on continuous functions, and we prove that the closed subsets of a zero-dimensional Polish space are well-quasi-ordered by bi-continuous embeddability.

scholarly journals Exhaustive operators and vector measures

1975 ◽  
Vol 19 (3) ◽  
pp. 291-300 ◽  
Author(s):  
N. J. Kalton
Keyword(s):  
Linear Operator ◽  
Vector Space ◽  
Compact Hausdorff Space ◽  
Hausdorff Space ◽  
Continuous Functions ◽  
Vector Measures ◽  
Borel Functions ◽  
Image Position ◽  
Real Topological Vector Space ◽  
Sequence Of Functions

Let S be a compact Hausdorff space and let Φ: C(S)→E be a linear operator defined on the space of real-valued continuous functions on S and taking values in a (real) topological vector space E. Then Φ is called exhaustive (7) if given any sequence of functions fn ∈ C(S) such that fn ≧ 0 andthen Φ(fn)→0 If E is complete then it was shown in (7) that exhaustive maps are precisely those which possess regular integral extensions to the space of bounded Borel functions on S; this is equivalent to possessing a representationwhere μ is a regular countably additive E-valued measure defined on the σ-algebra of Borel subsets of S.

scholarly journals Borel-amenable reducibilities for sets of reals

2009 ◽  
Vol 74 (1) ◽  
pp. 27-49 ◽  
Author(s):  
Luca Motto Ros
Keyword(s):  
Continuous Functions ◽  
Axiom Of Determinacy ◽  
Wadge Hierarchy ◽  
Borel Functions ◽  
Special Case

AbstractWe show that if ℱ is any “well-behaved” subset of the Borel functions and we assume the Axiom of Determinacy then the hierarchy of degrees on (ωω) induced by ℱ turns out to look like the Wadge hierarchy (which is the special case where ℱ is the set of continuous functions).

Boolean operations, Borel sets, and Hausdorff's question

1996 ◽  
Vol 61 (4) ◽  
pp. 1287-1304
Author(s):  
Abhijit Dasgupta
Keyword(s):  
Polish Space ◽  
Descriptive Set Theory ◽  
Boolean Operation ◽  
Boolean Operations ◽  
Borel Sets ◽  
Systematic Fashion ◽  
Borel Hierarchy ◽  
The Difference ◽  
Projective Hierarchy ◽  
Descriptive Set

The study of infinitary Boolean operations was undertaken by the early researchers of descriptive set theory soon after Suslin's discovery of the important operation. The first attempt to lay down their theory in a systematic fashion was the work of Kantorovich and Livenson [5], where they call these the analytical operations. Earlier, Hausdorff had introduced the δs operations — essentially same as the monotoneω-ary Boolean operations, and Kolmogorov, independently of Hausdorff, had discovered the same objects, which were used in his study of the R operator.The ω-ary Boolean operations turned out to be closely related to most of the classical hierarchies over a fixed Polish space X, including, e. g., the Borel hierarchy (), the difference hierarchies of Hausdorff (Dη()), the C-hierarchy (Cξ) of Selivanovski, and the projective hierarchy (): for each of these hierarchies, every level can be expressed as the range of an ω-ary Boolean operation applied to all possible sequences of open subsets of X. In the terminology of Dougherty [3], every level is “open-ω-Boolean” (if and are collections of subsets of X and I is any set, is said to be -I-Boolean if there exists an I-ary Boolean operation Φ such that = Φ, i. e. is the range of Φ restricted to all possible I-sequences of sets from ). If in addition, the space X has a basis consisting of clopen sets, then the levels of the above hierarchies are also “clopen-ω-Boolean.”

OCCUPATION TIMES OF BROWNIAN SEGMENTS AND THE σ-FINITE WIENER MEASURE

2005 ◽  
Vol 08 (02) ◽  
pp. 199-213
Author(s):  
TOMASZ BOJDECKI ◽  
LUIS G. GOROSTIZA
Keyword(s):  
Brownian Motion ◽  
Polish Space ◽  
Wiener Measure ◽  
Asymptotic Result ◽  
Main Role ◽  
Occupation Times ◽  
Borel Sets ◽  
New Information ◽  
Strengthened Form ◽  
Consecutive Time

We give an asymptotic result for the occupation of Borel sets of functions by the segments of recurrent Brownian motion on consecutive time intervals [n, n +1], n =0, 1, 2, …. This result provides new information on the behavior of Brownian motion, which is illustrated by examples. A formulation in terms of weak convergence of random measures on Polish space is also given. The proof is based on (a strengthened form of) the Darling–Kac occupation time theorem for Markov chains, and our result can be viewed as a "trajectorial" extension of that theorem. The main role in the occupation limit for Brownian segments is played by the σ-finite Wiener measure, which first appeared in a different context. An extension for segments of symmetric α-stable Lévy processes is also given.

The Complexity of Everywhere Divergent Fourier Series

1991 ◽  
Vol 43 (2) ◽  
pp. 413-424
Author(s):  
T. I. Ramsamujh
Keyword(s):  
Fourier Series ◽  
Unit Circle ◽  
Polish Space ◽  
Continuous Functions ◽  
Rank Function ◽  
Alternative Definition ◽  
Closed Sets ◽  
Natural Measure ◽  
Definition Of ◽  
Divergent Fourier Series

AbstractA natural rank function is defined on the set DS of everywhere divergent sequences of continuous functions on the unit circle T. The rank function provides a natural measure of the complexity of the sequences in DS, and is obtained by associating a well-founded tree with each such sequence. The set DF of everywhere divergent Fourier series, and the set DT of everywhere divergent trigonometric series with coefficients that tend to zero, can be viewed as natural subsets of DS. It is shown that the rank function is a coanalytic norm which is unbounded in ω1 on DF. From this it follows that DF, DT and DS are not Borel subsets of the Polish space SC(T) of all sequences of continuous functions on T. Finally an alternative definition of the rank function is formulated by using nested sequences of closed sets.

Measurable chromatic numbers

2008 ◽  
Vol 73 (4) ◽  
pp. 1139-1157 ◽  
Author(s):  
Benjamin D. Miller
Keyword(s):  
Chromatic Number ◽  
Equivalence Relation ◽  
Initial Segment ◽  
Polish Space ◽  
Borel Function ◽  
Chromatic Numbers ◽  
Unilateral Shift ◽  
Dichotomy Theorem ◽  
Borel Functions ◽  
Measurable Chromatic Number

AbstractWe show that if add(null) = c, then the globally Baire and universally measurable chromatic numbers of the graph of any Borel function on a Polish space are equal and at most three. In particular, this holds for the graph of the unilateral shift on [ℕ]ℕ, although its Borel chromatic number is ℵ0. We also show that if add(null) = c, then the universally measurable chromatic number of every treeing of a measure amenable equivalence relation is at most three. In particular, this holds for “the” minimum analytic graph with uncountable Borel (and Baire measurable) chromatic number. In contrast, we show that for all κ Є6 (2, 3…..ℵ0, c), there is a treeing of E0 with Borel and Baire measurable chromatic number κ. Finally, we use a Glimm–Effros style dichotomy theorem to show that every basis for a non-empty initial segment of the class of graphs of Borel functions of Borel chromatic number at least three contains a copy of (ℝ<ℕ, ⊇).

On Measures Determined by Continuous Functions that are not of Bounded Variation

1970 ◽  
Vol 13 (1) ◽  
pp. 121-124 ◽  
Author(s):  
J. H. W. Burry ◽  
H. W. Ellis
Keyword(s):  
Continuous Function ◽  
Total Variation ◽  
Bounded Variation ◽  
Real Line ◽  
Open Interval ◽  
Continuous Functions ◽  
Outer Measure ◽  
Function Of Bounded Variation ◽  
Borel Sets ◽  
Nondifferentiable Function

In [1] it was shown that a continuous function of bounded variation on the real line determined a Method II outer measure for which the Borel sets were measurable and the measure of an open interval was equal to the total variation of f over the interval. The monotone property of measures implied that if an open interval I on which f was not of bounded variation contained subintervals on which f was of finite but arbitrarily large total variation then the measure of I was infinite. Since there are continuous functions that are not of bounded variation over any interval (e.g. the Weierstrasse nondifferentiable function) the general case was not resolved.

On the Structure of Finite Level and ω-Decomposable Borel Functions

2013 ◽  
Vol 78 (4) ◽  
pp. 1257-1287 ◽  
Author(s):  
Luca Motto Ros
Keyword(s):  
Banach Space ◽  
Elementary Proof ◽  
Borel Function ◽  
Continuous Functions ◽  
Full Description ◽  
Countable Union ◽  
Space Theory ◽  
Measurable Functions ◽  
Borel Functions

AbstractWe give a full description of the structure under inclusion of all finite level Borel classes of functions, and provide an elementary proof of the well-known fact that not every Borel function can be written as a countable union of Σα0-measurable functions (for every fixed 1 ≤ α < ω1). Moreover, we present some results concerning those Borel functions which are ω-decomposable into continuous functions (also called countably continuous functions in the literature): such results should be viewed as a contribution towards the goal of generalizing a remarkable theorem of Jayne and Rogers to all finite levels, and in fact they allow us to prove some restricted forms of such generalizations. We also analyze finite level Borel functions in terms of composition of simpler functions, and we finally present an application to Banach space theory.

Some results about Borel sets in descriptive set theory of hyperfinite sets

1990 ◽  
Vol 55 (2) ◽  
pp. 604-614 ◽  
Author(s):  
Boško Živaljević
Keyword(s):  
Set Theory ◽  
Descriptive Set Theory ◽  
Counting Measure ◽  
Borel Sets ◽  
Similar Characterization ◽  
Borel Functions ◽  
Remarkable Result ◽  
Descriptive Set ◽  
The Given ◽  
Internal Sets

A remarkable result of Henson and Ross [HR] states that if a function whose graph is Souslin in the product of two hyperfinite sets in an ℵ1 saturated nonstandard universe possesses a certain nice property (capacity) then there exists an internal subfunction of the given one possessing the same property. In particular, they prove that every 1-1 Souslin function preserves any internal counting measure, and show that every two internal sets A and B with ∣A∣/∣B∣ ≈ 1 are Borel bijective. As a supplement to the last-mentioned result of Henson and Ross, Keisler, Kunen, Miller and Leth showed [KKML] that two internal sets A and B are bijective by a countably determined bijection if and only if ∣A∣/∣B∣ is finite and not infinitesimal.In this paper we first show that injective Borel functions map Borel sets into Borel sets, a fact well known in classical descriptive set theory. Then, we extend the result of Henson and Ross concerning the Borel bijectivity of internal sets whose quotient of cardinalities is infinitely closed to 1. We prove that two Borel sets, to which we may assign a counting measure not equal to 0 or ∞, are Borel bijective if and only if they have the same counting measure ≠0, ∞. This, together with the similar characterization for Souslin and measurable countably determined sets, extends the above-mentioned results from [HR] and [KKML].

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