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    Cauchy inequalities for Taylor coefficients

    FT-REHJT

    If $\abs{f}\le M$ on the circle $\abs{z-z_0}=R$, then the $n$th Taylor coefficient of $f$ at $z_0$ has modulus at most $M/R^n$.Suggest a slogan

    Let \(z_0\in\CC\) and \(R>0\), and let \(f\) be holomorphic on an open set containing the closed disc \(\abs{z-z_0}\le R\). Then for every integer \(n\ge0\), \[ \abs{f^{(n)} (z_0) \over n!} \leq R^{-n} \sup_{\abs{z-z_0}=R} \abs{f(z)}. \]

    State the Cauchy inequalities in the form bounding $\abs{f^{(n)}(z_0)/n!}$.

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