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In mathematics, an index set is a set whose members label (or index) members of another set.〔Munkres, James R. Topology. Vol. 2. Upper Saddle River: Prentice Hall, 2000.〕 For instance, if the elements of a set ''A'' may be ''indexed'' or ''labeled'' by means of a set ''J'', then ''J'' is an index set. The indexing consists of a surjective function from ''J'' onto ''A'' and the indexed collection is typically called an ''(indexed) family'', often written as (''A''''j'')''j''∈''J''. ==Examples== *An enumeration of a set gives an index set , where is the particular enumeration of . *Any countably infinite set can be indexed by . *For , the indicator function on is the function given by : The set of all the functions is an uncountable set indexed by . 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「index set」の詳細全文を読む スポンサード リンク
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