Computable topological presentations - Department of Formal methods
Pré-Publication, Document De Travail Année : 2024

Computable topological presentations

Résumé

A computable topological presentation of a space is given by an effective list of a countable basis of non-empty open sets so that the intersection of the basic sets is uniformly effectively enumerable. We show that every countably based T0-space has a computable topological presentation, and that, conversely, every (formal) computable topological presentation represents some Polish space. In the compact case, we give a computable uniform list of computable topological presentations such that every compact Polish space is represented by exactly one presentation from the list. Note that none of these results assume that the Polish (or T0) spaces are effective. Quite surprisingly, the effectively compact topological presentations turn out to be rather well behaved. Not only do such presentations allow one to construct a Delta02 (complete) metric compatible with the topology, but also, under a mild extra condition, they can be turned into a computably compact Polish presentation of the space.
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Dates et versions

hal-04848634 , version 1 (19-12-2024)

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  • HAL Id : hal-04848634 , version 1

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Mathieu Hoyrup, Alexander Melnikov, Keng Meng Ng. Computable topological presentations. 2024. ⟨hal-04848634⟩
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