Editing Index set (section)

{{Short description|Mathematical term}}
{{distinguish|text = [[Indexed set|index'''ed''' sets]], or [[Index set (recursion theory)|index sets in computability theory]]}}
In [[mathematics]], an '''index set''' is a set whose members label (or index) members of another set.<ref>{{cite web|last=Weisstein|first=Eric|title=Index Set|url=http://mathworld.wolfram.com/IndexSet.html|work=Wolfram MathWorld|publisher=Wolfram Research|access-date=30 December 2013}}</ref><ref>{{cite book|last=Munkres|first=James R.|title=Topology|volume= 2|location=Upper Saddle River|publisher=Prentice Hall|year=2000}}</ref> For instance, if the elements of a [[Set (mathematics)|set]] {{mvar|A}} may be ''indexed'' or ''labeled'' by means of the elements of a set {{mvar|J}}, then {{mvar|J}} is an index set. The indexing consists of a [[surjective function]] from {{mvar|J}} onto {{mvar|A}}, and the indexed collection is typically called an ''[[indexed family]]'', often written as {{math|{''A''<sub>''j''</sub>}<sub>''j''∈''J''</sub>}}.