 ##  [Cardinality](/cardinality) 

  ##  [Cardinality](https://natural.quantumdictionary.io/cardinality-0) 

  
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**Natural &amp; Formal Sciences Dictionary**

 
Definition

Cardinality is a measure of the number of elements in a set: finite sets have a natural finite cardinal, infinite sets are compared by the existence of bijections (same cardinality) or injections/surjections (≤ relation).

 
 ##  [Cardinality](https://mathlogic.quantumdictionary.io/cardinality-1) 

  
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- Natural &amp; Formal Sciences -

**Mathematics &amp; Logic Dictionary**

 
Definition

The cardinality of a set is the equivalence class of sets equipotent (in bijection) to it; cardinality measures size up to bijection and distinguishes finite sizes and infinite sizes indexed by cardinals such as ℵ_0 or 2^{ℵ_0}.