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A geometric extension of Schwarz’s Lemma and applications. (English) Zbl 1334.30010

Summary: Let \(f\) be a holomorphic function of the unit disc \(\mathbb{D}\), preserving the origin. According to Schwarz’s Lemma, \(|f^{\prime}(0)|\leq1\), provided that \(f(\mathbb{D})\subset\mathbb{D}\). We prove that this bound still holds, assuming only that \(f(\mathbb{D})\) does not contain any closed rectilinear segment \([0,e^{i\phi}]\), \(\phi \in[0,2\pi]\), i.e., does not contain any entire radius of the closed unit disc. Furthermore, we apply this result to the hyperbolic density and we give a covering theorem.

MSC:

30C80 Maximum principle, Schwarz’s lemma, Lindelöf principle, analogues and generalizations; subordination
30C25 Covering theorems in conformal mapping theory
30C99 Geometric function theory
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