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    Fixed points of analytic self-maps of the disk

    P-TIE-F11-11

    Area
    Complex Analysis
    Status
    draft
    Contents

    Let \(g\) be analytic for \(\abs{z} \le 1\) and \(\abs{g(z)} < 1\) for \(\abs{z} = 1\).

    1. Show that \(g\) has a unique fixed point in \(\abs{z} < 1\).

    2. What happens if we replace \(\abs{g(z)} < 1\) with \(\abs{g(z)} \le 1\) for \(\abs{z} = 1\)? Give an example if (a) is not true or give an proof if (a) is still true.

    3. What happens if we simply assume that \(f\) is analytic for \(\abs{z} < 1\) and \(\abs{f(z)} < 1\) for \(\abs{z} < 1\)? Suppose that \(f(z) \not\equiv z\). Can \(f\) have more than one fixed point in \(\abs{z} < 1\)?

    Hint: The map \(\psi_\alpha(z) = \frac{\alpha - z}{1 - \bar{\alpha} z}\) may be useful.

    Solution submission

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