We introduce the notion of quasi-zero-dimensionality as a substitute for the notion of zero-dimensionality, motivated by the fact that the latter behaves badly in the realm of qcb-spaces. We prove that the category $\QZ$ of quasi-zero-dimensional qcb$_0$-spaces is cartesian closed. Prominent examples of spaces in $\QZ$ are the spaces in the sequential hierarchy of the Kleene-Kreisel continuous functionals. Moreover, we characterise some types of closed subsets of $\QZ$-spaces in terms of their ability to allow extendability of continuous functions. These results are related to an open problem in Computable Analysis.
@InProceedings{schroder:OASIcs.CCA.2009.2274, author = {Schr\"{o}der, Matthias}, title = {{A Note on Closed Subsets in Quasi-zero-dimensional Qcb-spaces}}, booktitle = {6th International Conference on Computability and Complexity in Analysis (CCA'09)}, pages = {233--244}, series = {Open Access Series in Informatics (OASIcs)}, ISBN = {978-3-939897-12-5}, ISSN = {2190-6807}, year = {2009}, volume = {11}, editor = {Bauer, Andrej and Hertling, Peter and Ko, Ker-I}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.CCA.2009.2274}, URN = {urn:nbn:de:0030-drops-22748}, doi = {10.4230/OASIcs.CCA.2009.2274}, annote = {Keywords: Computable analysis, Qcb-spaces, extendability} }
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