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Дата последнего поиска статьи во внешних источниках: 30 марта 2016 г.
Аннотация:Using the Gandy-Harrington topology and other methods of effective descriptive set theory, we prove several theorems about compact and σ-compact sets. In particular, it is proved that any Δ11 -set A in the Baire space N either is an at most countable union of compact Δ11 -sets (and hence is σ-compact) or contains a relatively closed subset homeomorphic to N (in this case, of course, A cannot be σ-compact).