Abstract
In the recent paper [BFP], Balogh-Fässler-Platis proved that a spiral-stretch map is extremal for the extremal problem
among the set of all \(\mathbb{W}_{\rm{loc}}^{1,2}\)-homeomorphisms g with finite linear distortion K(w, g) between two annuli A1 and A2 and having the same boundary values with the spiral-stretch map. In this short note, we will give a very fast approach to this result without the \(\mathbb{W}_{\rm{loc}}^{1,2}\)-assumption. Furthermore, the unique extremality of a spiral-stretch map is also obtained.
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The authors would like to thank the referee for a very careful reading of the manuscript and for several corrections.
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Research supported by the National Natural Science Foundation of China and the Natural Science Foundation of Jiangsu Province.
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Feng, X., Hu, Y. & Shen, Y. A note on the unique extremality of spiral-stretch maps. JAMA 138, 465–472 (2019). https://doi.org/10.1007/s11854-019-0039-1
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DOI: https://doi.org/10.1007/s11854-019-0039-1