Tytuł pozycji:
Difference functions of periodic measurable functions
- Tytuł:
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Difference functions of periodic measurable functions
- Autorzy:
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Keleti, Tamás
- Powiązania:
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https://bibliotekanauki.pl/articles/1205348.pdf
- Data publikacji:
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1998
- Wydawca:
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Polska Akademia Nauk. Instytut Matematyczny PAN
- Źródło:
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Fundamenta Mathematicae; 1998, 157, 1; 15-32
0016-2736
- Język:
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angielski
- Prawa:
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Wszystkie prawa zastrzeżone. Swoboda użytkownika ograniczona do ustawowego zakresu dozwolonego użytku
- Dostawca treści:
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Biblioteka Nauki
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Przejdź do źródła  Link otwiera się w nowym oknie
We investigate some problems of the following type: For which sets H is it true that if f is in a given class ℱ of periodic functions and the difference functions $Δ_h f(x)=f(x+h)-f(x)$ are in a given smaller class G for every h ∈ H then f itself must be in G? Denoting the class of counter-example sets by ℌ(ℱ,G), that is, $ℌ(ℱ,G) = {H ⊂ ℝ/ℤ : (∃f ∈ ℱ \ G) (∀ h ∈ H) Δ_h f ∈ G}$, we try to characterize ℌ(ℱ,G) for some interesting classes of functions ℱ ⊃ G. We study classes of measurable functions on the circle group $\mathbb{T}=ℝ/ℤ$ that are invariant for changes on null-sets (e.g. measurable functions, $L_p$, $L_∞$, essentially continuous functions, functions with absolute convergent Fourier series (ACF*), essentially Lipschitz functions) and classes of continuous functions on $\mathbb{T}$ (e.g. continuous functions, continuous functions with absolute convergent Fourier series, Lipschitz functions). The classes ℌ(ℱ,G) are often related to some classes of thin sets in harmonic analysis (e.g. $ℌ(L_1,{ACF}*)$ is the class of N-sets). Some results concerning the difference property and the weak difference property of these classes of functions are also obtained.