Abstract
We continue to study upper sets \({\widetilde{A}=\{(x,r)\in A\times R_+ :\exists y\in A\setminus\{x\}, r=|x-y|\}}\) equipped by hyperbolic metric. We define analogous of quasiconvexity, simply connectedness and nearlipschitz functions. We give a new definition of quasisymmetry as nearlipschitz characteristic on \({\widetilde{A}}\). In the final part in terms of upper sets we give the following extension property of \({A\subset R^2}\). For \({0\le\varepsilon\le \delta}\), each \({(1+\varepsilon)}\)-bilipschitz map f : A → R 2 has an extension to a \({(1+C\varepsilon)}\)-bilipschitz map F : R 2 → R 2.
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Communicated by Matti Vuorinen.
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Trotsenko, D.A. Extendability of Classes of Maps and New Properties of Upper Sets. Complex Anal. Oper. Theory 5, 967–984 (2011). https://doi.org/10.1007/s11785-010-0096-z
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DOI: https://doi.org/10.1007/s11785-010-0096-z