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Characterizing Lipschitz images of injective metric spaces. arXiv:2405.01860

Preprint, arXiv:2405.01860 [math.GN] (2024).
Summary: A metric space \(X\) is {\em injective} if every non-expanding map \(f:B\to X\) defined on a subspace \(B\) of a metric space \(A\) can be extended to a non-expanding map \(\bar f:A\to X\). We prove that a metric space \(X\) is a Lipschitz image of an injective metric space if and only if \(X\) is Lipschitz connected in the sense that for every points \(x,y\in X\), there exists a Lipschitz map \(f:[0,1]\to X\) such that \(f(0)=x\) and \(f(1)=y\). In this case the metric space \(X\) carries a well-defined intrinsic metric. A metric space \(X\) is a Lipschitz image of a compact injective metric space if and only if \(X\) is compact, Lipschitz connected and its intrinsic metric is totally bounded. A metric space \(X\) is a Lipschitz image of a separable injective metric space if and only if \(X\) is a Lipschitz image of the Urysohn universal metric space if and only if \(X\) is analytic, Lipschitz connected and its intrinsic metric is separable.

MSC:

54E35 Metric spaces, metrizability
54E40 Special maps on metric spaces
51F30 Lipschitz and coarse geometry of metric spaces
54C55 Absolute neighborhood extensor, absolute extensor, absolute neighborhood retract (ANR), absolute retract spaces (general properties)
54E45 Compact (locally compact) metric spaces
54E50 Complete metric spaces
54F15 Continua and generalizations
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