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Steklov Mathematical Institute Seminar
June 4, 2009 16:00, Moscow, Steklov Mathematical Institute of RAS, Conference Hall (8 Gubkina)


Differentiation of measurable functions and Whitney–Lusin's type structure theorems

B. Bojarski

Institute of Mathematics of the Polish Academy of Sciences


http://youtu.be/wNMiMDEkJ3U

Abstract: Given a measurable subset $P\subset\mathbb R^n$ of possitive $n$-measure the notion of $k$-quasismooth functions $f\colon P\to\mathbb R$ is defined, $k\ge 0$, $k$-integer. This class is characterized in terms of approximate $k$-th order total Peano differentiablity at almost every point of $P$. For $k=0$ we obtain the Egorov–Denjoy–Lusin structure theory of measurable functions. The case $k\ge 1$ connects Lusin's theory with H. Whitney's theory of $k$-smooth functions on arbitrary closed subsets of $\mathbb R^n$. Applications to harmonic analysis, singular integrals, potential theory and PDE will be given.


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