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arXiv 2004.11631math.FA
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巴拿赫空间上的群不变分离多项式

Group invariant separating polynomials on a Banach space

Javier Falco, Domingo Garcia, Mingu Jung, Manuel Maestre

摘要:

本文研究了巴拿赫空间$X$上的群不变连续多项式,该多项式将给定的集合$K$在$X$内,并将点$z$在$K$外.证明了:如果$X$是实巴拿赫空间,$G$是$\mathcal{L} (X)$的紧群,$K$是$X$中的$G$不变集,$z$是$K$外的一个点,它可以通过一个连续多项式$Q$与$K$分离,那么$z$也可以通过一个$G$不变连续多项式$P$与$K$分离.当$X$是复巴拿赫空间时,这一结果不成立,因此我们给出了一些附加的条件以得到复情形下的类似结果.在假设$X$具有Schauder基的条件下,我们还得到了分离定理,并将其应用于几个典型群.在这种情况下,我们得到的点,可以从封闭的单位球的群不变多项式分离的特征。

英文摘要:

We study the group invariant continuous polynomials on a Banach space $X$ that separate a given set $K$ in $X$ and a point $z$ outside $K$. We show that if $X$ is a real Banach space, $G$ is a compact group of $\mathcal{L} (X)$, $K$ is a $G$-invariant set in $X$, and $z$ is a point outside $K$ that can be separated from $K$ by a continuous polynomial $Q$, then $z$ can also be separated from $K$ by a $G$-invariant continuous polynomial $P$. It turns out that this result does not hold when $X$ is a complex Banach space, so we present some additional conditions to get analogous results for the complex case. We also obtain separation theorems under the assumption that $X$ has a Schauder basis which give applications to several classical groups. In this case, we obtain characterizations of points which can be separated by a group invariant polynomial from the closed unit ball.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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