Minimising Hausdorff Dimension under Hölder Equivalence
We study the infimal value of the Hausdorff dimension of spaces that are Hölder equivalent to a given metric space; we call this bi-Hölder-invariant "Hölder dimension". This definition and some of our methods are analogous to those used in the study of conformal dimension. We prove that Hölder dimension is bounded above by capacity dimension for compact, doubling metric spaces. As a corollary, we obtain that Hölder dimension is equal to topological dimension for compact, locally self-similar metric spaces. In the process, we show that any compact, doubling metric space can be mapped into Hilbert space so that the map is a bi-Hölder homeomorphism onto its image and the Hausdorff dimension of the image is arbitrarily close to the original space's capacity dimension. We provide examples to illustrate the sharpness of our results. For instance, one example shows Hölder dimension can be strictly greater than topological dimension for non-self-similar spaces, and another shows the Hölder dimension need not be attained.