Abstract
For a separable Hilbert space E whose dimension is ≥2 and for an open subset Ω of E, not empty and different from E, let \(\mathcal{M}\) be the set of all points of Ω which have at least two projections on the close set E\Ω, and let \(\mathcal{N}\) be the set of all the centres of the open balls contained in Ω and which are maximal for inclusion. We show that the Hausdorff dimension dimH(\(\mathcal{N}\)\\(\mathcal{M}\)) of \(\mathcal{N}\)\\(\mathcal{M}\) may be any real value s such that 0≤s≤dim E; we also show that Ω can be chosen so that \(\mathcal{N}\) is everywhere dense in Ω and so that we have dimH(\(\mathcal{N}\)\\(\mathcal{M}\))=1.
Associons à un ouvert Ω d'un espace de Hilbert séparable E de dimension ≥2, non vide et distinct de E, l'ensemble \(\mathcal{M}\) des points de Ω admettant plusieurs projections sur le fermé E\Ω, et l'ensemble \(\mathcal{N}\) des centres des boules ouvertes inclues dans Ω et maximales pour l'inclusion. Nous montrons d'une part que la dimension de Hausdorff dimH(\(\mathcal{N}\)\\(\mathcal{M}\)) de \(\mathcal{N}\)\\(\mathcal{M}\) peut prendre toute valeur réelle s telle que 0≤s≤dim E, et d'autre part qu'on peut choisir Ω de sorte que \(\mathcal{N}\) soit dense dans Ω et qu'on ait dimH(\(\mathcal{N}\)\\(\mathcal{M}\))=1.
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Rivière, A. Dimension de Hausdorff de la Nervure. Geometriae Dedicata 85, 217–235 (2001). https://doi.org/10.1023/A:1010310524706
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DOI: https://doi.org/10.1023/A:1010310524706