##  [Index of a Subgroup](/index-subgroup) 

  ##  [Index of a Subgroup](https://puremath.quantumdictionary.io/index-subgroup-0) 

  

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- Mathematics & Logic -

**Pure Mathematics Dictionary**

 







 

 

 

 



 

 

 

 

Definition

The cardinal number of the set of left cosets (equivalently right cosets) of a subgroup H in a group G; it measures the relative size of H inside G and is finite when G decomposes into finitely many cosets of H.