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The packing measure of the graphs and level sets of certain continuous functions. (English) Zbl 0657.28006

It is well-known that if f: [a,b]\(\to {\mathbb{R}}\) is Hölder-continuous with exponent \(\alpha\), its graph has Hausdorff dimension at most 2- \(\alpha\) and almost all of its level sets \(f^{-1}\{x\}\) have Hausdorff dimension at most 1-\(\alpha\). The author studies the problem of getting lower bounds using packing measures and dimension instead those of Hausdorff. He shows that if \(\xi\) is a non-decreasing function with \(\xi (0)=0\) and if f satisfies \[ \limsup_{h\to 0}| f(t+h)\quad -\quad f(t)| /\xi (| h|)\quad >\quad 0 \] for almost all t, then the \(\phi\)-packing measure of the graph of f is infinite for any non- decreasing \(\phi\) growing more slowly than \(t^ 2/\xi (t)\). Also if \(\psi\) grows more slowly than t/\(\xi\) (t), the level sets \(f^{-1}\{x\}\) have infinite \(\psi\)-packing measure except for values x in some first category set. Here the first category cannot be replaced by Lebesgue measure zero.
Reviewer: P.Mattila

MSC:

28A75 Length, area, volume, other geometric measure theory
26A15 Continuity and related questions (modulus of continuity, semicontinuity, discontinuities, etc.) for real functions in one variable
26A16 Lipschitz (Hölder) classes
Full Text: DOI

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