Sobolev mappings: Lipschitz density is not an isometric invariant of the target

Abstract

If $M$ is a compact smooth manifold and $X$ is a compact metric space, the Sobolev space $W^{1,p}(M,X)$ is defined through an isometric embedding of $X$ into a Banach space. We prove that the answer to the question whether Lipschitz mappings $\mathrm{Lip}(M,X)$ are dense in $W^{1,p}(M,X)$ may depend on the isometric embedding of the target.

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