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Transactions of the American Mathematical Society

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Holomorphic extensions from open families of circles


Author: Josip Globevnik
Journal: Trans. Amer. Math. Soc. 355 (2003), 1921-1931
MSC (2000): Primary 30E20
DOI: https://doi.org/10.1090/S0002-9947-03-03241-0
Published electronically: January 8, 2003
MathSciNet review: 1953532
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Abstract: For a circle $\Gamma =\{ z\in \mathbb{C}\colon \vert z-c\vert=\rho \}$ write $\Lambda (\Gamma )=\{ (z,w)\colon (z-a)(w-\overline{a}) =\rho ^{2}, 0<\vert z-a\vert<\rho \}$. A continuous function $f$ on $\Gamma $ extends holomorphically from $\Gamma $(into the disc bounded by $\Gamma $) if and only if the function $F(z,\overline{z})=f(z)$ defined on $\{(z,\overline{z})\colon z\in \Gamma \}$ has a bounded holomorphic extension into $\Lambda (\Gamma )$. In the paper we consider open connected families of circles $\mathcal{C}$, write $U=\bigcup \{ \Gamma \colon \Gamma \in \mathcal{C}\}$, and assume that a continuous function on $U$ extends holomorphically from each $\Gamma \in \mathcal{C}$. We show that this happens if and only if the function $F(z, \overline{z})=f(z)$ defined on $\{ (z,\overline{z})\colon z\in U\}$ has a bounded holomorphic extension into the domain $\bigcup \{ \Lambda (\Gamma )\colon \Gamma \in \mathcal{Q}\}$ for each open family $\mathcal{Q}$ compactly contained in $\mathcal{C}$. This allows us to use known facts from several complex variables. In particular, we use the edge of the wedge theorem to prove a theorem on real analyticity of such functions.


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Additional Information

Josip Globevnik
Affiliation: Institute of Mathematics, Physics and Mechanics, University of Ljubljana, Ljubljana, Slovenia
Email: josip.globevnik@fmf.uni-lj.si

DOI: https://doi.org/10.1090/S0002-9947-03-03241-0
Received by editor(s): July 24, 2002
Published electronically: January 8, 2003
Dedicated: Dedicated to Professor Ivan Vidav on the occasion of his eighty-fifth birthday
Article copyright: © Copyright 2003 American Mathematical Society

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