Ballmann, Werner Max Planck Institute for Mathematics, Max Planck Society;
Polymerakis, Panagiotis Max Planck Institute for Mathematics, Max Planck Society;
https://dx.doi.org/10.4310/SDG.2018.v23.n1.a1 (出版社版)
https://doi.org/10.48550/arXiv.1911.04371 (プレプリント)
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