##  [Axiom of Extensionality](/index.php/axiom-extensionality) 

  ##  [Axiom of Extensionality](https://natural.quantumdictionary.io/axiom-extensionality-0) 

  

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**Natural & Formal Sciences Dictionary**

 







 

 

 

 



 

 

 

 

Definition

A foundational axiom of (standard) set theory stating that two sets are identical precisely when they have the same elements: for any sets A and B, A = B iff every x is a member of A exactly when x is a member of B.