Darboux like functions that are characterizable by images, preimages and associated sets (Q1978880)

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scientific article; zbMATH DE number 1449435
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Darboux like functions that are characterizable by images, preimages and associated sets
scientific article; zbMATH DE number 1449435

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    Darboux like functions that are characterizable by images, preimages and associated sets (English)
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    21 May 2000
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    The class \(\mathcal F\) of functions is characterizable by images (preimages, respectively), if there exist two systems \(\mathcal A\) and \(\mathcal B\) of subsets of \(\mathbb R\) such that \[ \begin{aligned} \mathcal F &= \{f:\mathbb R \to \mathbb R;\;\forall A \in \mathcal A:\;f(A) \in \mathcal B\} \\ (\mathcal F &= \{f:\mathbb R \to \mathbb R;\;\forall B \in \mathcal B:\^^Mf^{-1}(B) \in \mathcal A\}, \text{respectively}). \end{aligned} \] They show which classes of Darboux-like functions (e.g., almost continuous functions, connectivity functions, etc.) are characterizable by images (preimages, respectively) and which are not. It is also shown that the class of Sierpiński-Zygmund functions can be characterized neither by images nor preimages. (A function \(f\) is a Sierpiński-Zygmund function if a restriction \(f|Y\) is discontinuous whenever \(Y \subset \mathbb R\) is a set of cardinality continuum).
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    Darboux functions
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    extendable functions
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    almost continuous functions
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    connectivity functions
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    functions with perfect road
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    peripherally continuous functions
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    DIVP-functions
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    SCIVP-functions
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    WCIVP-functions
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    Sierpiński-Zygmund functions
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    associated sets
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