On the Converse of Shimoda's Theorem

We study Shimoda's theorem on the holomorphicity of a function $f(z,w)$ defined in a bidisc $U\times V=\left\{ \left| z \right|<1 \right\}\times \left\{ \left| w \right|<1 \right\},$ which is holomorphic with respect to $w\in V$ for each fixed $z\in U$ and is holomorphic with respect to $z\in U$ for each fixed $w\in E$, where $E\subset V$ is a countable set with at least one limit point in $V$. Shimoda proved that in this case $f(z,w)$ is holomorphic in $U\times V$ except for a nowhere dense closed subset of $U\times V$. We prove a converse: for any relatively closed nowhere dense set $S\subset U$ such that $\partial U\bigcup S$ is connected, there exists a function satisfying the conditions of Shimoda's theorem that is holomorphic in $(U\setminus S)\times V$ and doesn't extend holomorphically to any point of $S\times V$.

Authors

Publication Details

Journal
arXiv (Cornell University)
Published
2026-10-29
DOI
https://doi.org/10.48550/arxiv.2610.40381
Primary Topic
Holomorphic and Operator Theory
Type
preprint
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preprint

On the Converse of Shimoda's Theorem

Rasulov Kamol, Sevdiyor Imomkulov
arXiv (Cornell University)
Holomorphic and Operator Theory
preprint

On the Converse of Shimoda's Theorem

Rasulov Kamol, Sevdiyor Imomkulov
preprint en

Abstract

We study Shimoda's theorem on the holomorphicity of a function $f(z,w)$ defined in a bidisc $U\times V=\left\{ \left| z \right|<1 \right\}\times \left\{ \left| w \right|<1 \right\},$ which is holomorphic with respect to $w\in V$ for each fixed $z\in U$ and is holomorphic with respect to $z\in U$ for each fixed $w\in E$, where $E\subset V$ is a countable set with at least one limit point in $V$. Shimoda proved that in this case $f(z,w)$ is holomorphic in $U\times V$ except for a nowhere dense closed subset of $U\times V$. We prove a converse: for any relatively closed nowhere dense set $S\subset U$ such that $\partial U\bigcup S$ is connected, there exists a function satisfying the conditions of Shimoda's theorem that is holomorphic in $(U\setminus S)\times V$ and doesn't extend holomorphically to any point of $S\times V$.

arXiv (Cornell University)
Holomorphic and Operator Theory
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