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In mathematics, piecewise syndeticity is a notion of largeness of subsets of the natural numbers. A set is called ''piecewise syndetic'' if there exists a finite subset ''G'' of such that for every finite subset ''F'' of there exists an such that : where . Equivalently, ''S'' is piecewise syndetic if there are arbitrarily long intervals of where the gaps in ''S'' are bounded by some constant ''b''. == Properties == * A set is piecewise syndetic if and only if it is the intersection of a syndetic set and a thick set. * If ''S'' is piecewise syndetic then ''S'' contains arbitrarily long arithmetic progressions. * A set ''S'' is piecewise syndetic if and only if there exists some ultrafilter ''U'' which contains ''S'' and ''U'' is in the smallest two-sided ideal of , the Stone–Čech compactification of the natural numbers. * Partition regularity: if is piecewise syndetic and , then for some , contains a piecewise syndetic set. (Brown, 1968) * If ''A'' and ''B'' are subsets of , and ''A'' and ''B'' have positive upper Banach density, then is piecewise syndetic〔R. Jin, (Nonstandard Methods For Upper Banach Density Problems ), ''Journal of Number Theory'' 91, (2001), 20-38.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Piecewise syndetic set」の詳細全文を読む スポンサード リンク
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