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In mathematics, the Arens–Fort space is a special example in the theory of topological spaces, named for Richard Friederich Arens and M. K. Fort, Jr. Let ''X'' be a set of ordered pairs of non-negative integers (''m'', ''n''). A subset ''U'' of ''X'' is open if and only if: *it does not contain (0, 0), or *it contains (0, 0), and all but a finite number of points of all but a finite number of columns, where a column is a set with fixed ''m''. In other words, an open set is only "allowed" to contain (0, 0) if only a finite number of its columns contain significant gaps. By a significant gap in a column we mean the omission of an infinite number of points. It is * Hausdorff * regular * normal It is not: * second-countable * first-countable * metrizable * compact ==See also== * Fort space 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Arens–Fort space」の詳細全文を読む スポンサード リンク
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