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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. LOMI, 1979 Volume 92, Pages 60–84 (Mi znsl3190)

This article is cited in 1 paper

The simultaneous approximation by polynomials on the circle and in the interior of the disc

A. L. Vol'berg


Abstract: The subject of this paper is the investigation of the question whether the polynomials form a dense set in the space $L^2(h)\oplus L^2(\mu_{\mathbb D})$ where $h$ is a weight on the unit circle $\mathbb T$ and $\mu_{\mathbb D}$ is a measure in the unit disc $\mathbb D$. In the case $\operatorname{supp}\mu_{\mathbb D}\subset[0,1]$ some necessary and some (close) sufficient conditions for the answer to be positive are obtained (these conditions say, roughly speaking, thet the functions $\mu_{\mathbb D}(1-\delta,1)$ and $h(e^{i\Theta})$ tend to zero sufficiently rapidly as $\delta\to0$ and $\Theta\to0$). In the general case only sufficient conditions are given.

UDC: 517.5



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