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arXiv math/0407133math.CV
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关于Denjoy-Wolff定理的点态收敛性

Pointwise convergence on the boundary in the Denjoy-Wolff Theorem

Pietro Poggi-Corradini

摘要:

如果$ϕ$是圆盘的解析自映射(不是椭圆自同构),则Denjoy-Wolff定理预言存在一个点$p$和$|p|\leq 1$,使得迭代$ϕ_{n}$在圆盘的紧致子集上一致收敛到$p$。由于这些迭代都是有界的解析函数,所以存在全线性测度的单位圆的一个子集,在那里它们都是定义良好的。我们解决的问题,是否收敛到$p$仍然持有几乎处处的单位圆。答案取决于$p$的位置和$ϕ$的动力学性质。证明了当$|p|<1$(椭圆情形),逐点a.e.当且仅当$ϕ$不是内部函数时收敛成立。当$|p|=1$的事情更微妙。我们证明了当$ϕ$是双曲型或I型抛物型时,则点态a.e.收敛总是存在的。最后一种情况下,II型抛物仍然开放在这一刻,但我们猜想的答案是在椭圆形的情况下。

英文摘要:

If $ϕ$ is an analytic selfmap of the disk (not an elliptic automorphism) the Denjoy-Wolff Theorem predicts the existence of a point $p$ with $|p|\leq 1$ such that the iterates $ϕ_{n}$ converge to $p$ uniformly on compact subsets of the disk. Since these iterates are bounded analytic functions, there is a subset of the unit circle of full linear measure where they all well-defined. We address the question of whether convergence to $p$ still holds almost everywhere on the unit circle. The answer depends on the location of $p$ and the dynamical properties of $ϕ$. We show that when $|p|<1$(elliptic case), pointwise a.e. convergence holds if and only if $ϕ$ is not an inner function. When $|p|=1$ things are more delicate. We show that when $ϕ$ is hyperbolic or type I parabolic, then pointwise a.e. convergence holds always. The last case, type II parabolic remains open at this moment, but we conjecture the answer to be as in the elliptic case.

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