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zbMATH Open
Article . 2006
Data sources: zbMATH Open
Journal of Applied Analysis
Article . 2006 . Peer-reviewed
Data sources: Crossref
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Products of Strong Świa̧tkowski Functions

Products of strong Świątkowski functions
Authors: Szczuka, P.;

Products of Strong Świa̧tkowski Functions

Abstract

A function \(f\) is said to be a strong Świątkowski function if whenever \(\alpha , \beta \in I\) and \( y \in I(f(\alpha),f(\beta))\), there is an \(x_0 \in I(\alpha,\beta) \cap C(f)\) such that \(f(x_0) = y\) where \(I\) is a nondegenerate interval, \(I(a,b) = (a,b)\) if \(a < b\) and \((b,a)\) otherwise and \(C(f)\) denotes the set of all points of continuity of \(f\). One can easily see that strong Świątkowski functions are both Darbaux and quasi-continuous. Till now some research have been done to investigate which functions can or cannot be written as the product of a finite number of such functions and when it can be written what is the number of such functions in the product. For example, the sign function can be written as the product of three strong Świątkowski functions but it cannot be written as the product of two such functions. In an earlier paper the author has already shown that there is a function which can be written as the product of four such functions but cannot be written as the product of three. In this paper, he continues this investigation and finds a characterisation of the product of four or more strong Świątkowski functions. In his main result he proves that a function \(f\) is the product of four or more such functions if and only if the function \(f\) is cliquish, the set \([f = 0] = \{x \in I : f(x) =0\}\) is simply open, and there is a \(G_\delta\)-set \(A \subset [f = 0]\) such that for all \(a,b \in R\), if \(f(a)f(b) <0\), then \(A \cap I(a,b) \neq \emptyset\). The author also proves several interesting lemmas which are finally used to prove the main result.

Keywords

product of functions, cliquish, Continuity and related questions (modulus of continuity, semicontinuity, discontinuities, etc.) for real functions in one variable, quasi continuous, Real-valued functions in general topology, Darbaux functions

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
1
Average
Average
Average
bronze