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FINITE FLAT SPACES
Published online by Cambridge University Press: 14 August 2019
Abstract
We say that a finite metric space $X$ can be embedded almost isometrically into a class of metric spaces $C$ if for every $\unicode[STIX]{x1D716}>0$ there exists an embedding of $X$ into one of the elements of $C$ with the bi-Lipschitz distortion less than $1+\unicode[STIX]{x1D716}$. We show that almost isometric embeddability conditions are equal for the following classes of spaces.
(a) Quotients of Euclidean spaces by isometric actions of finite groups.
(b) $L_{2}$-Wasserstein spaces over Euclidean spaces.
(c) Compact flat manifolds.
(d) Compact flat orbifolds.
(e) Quotients of connected compact bi-invariant Lie groups by isometric actions of compact Lie groups. (This one is the most surprising.)
We call spaces which satisfy these conditions finite flat spaces. Since Markov-type constants depend only on finite subsets, we can conclude that connected compact bi-invariant Lie groups and their quotients have Markov type 2 with constant 1.
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- Copyright © University College London 2019