A K\documentclass[12pt]{minimal}
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\begin{document}$$K$$\end{document}-quasiconformal selfmap of the unit disk with identity boundary values satisfies the Hölder estimate |f(z)-f(w)|≤41-1/K|z-w|1/K.\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} |f(z)-f(w)| \le 4^{1-1/K} |z-w|^{1/K}. \end{aligned}$$\end{document}The constant 41-1/K\documentclass[12pt]{minimal}
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\begin{document}$$4^{1-1/K}$$\end{document} is sharp.