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日時：12月22日(木)15:30-17:00 場所：名古屋大学大学院情報科学研究科棟322号室 講演者：Franklin D. Tall (トロント大学) 題目：Definable versions of Hurewicz’ conjecture アブストラクト： A topological space is Menger if, given a countable sequence of open covers, there is a finite selection from each of them, so that the union of the selections is a cover. The Menger property lies strictly between \sigma-compactness and Lindelofness. In 1925 Hurewicz conjectured that Menger was equivalent to \sigma-compact in metrizable spaces. This was refuted by Chaber and Pol in 2002. However, for spaces which are in some sense "definable", the situation is less clear. Our principal result (joint with S. Todorcevic and S. Tokgoz) is that Hurewicz' Conjecture for projective sets of reals is equiconsistent with an inaccessible cardinal. In general topological spaces, the situation is more complicated, but we have a variety of similar results for co-analytic spaces, i.e. spaces having Cech-Stone remainders which are continuous images of the space of irrationals.