Axiom:Axiom of Extension (Classes)

Axiom
Two classes are equal if they contain the same elements:


 * $\forall x: \left({x \in A \iff x \in B}\right) \iff A = B$

The order of the elements in the sets is immaterial.

Also known as
Otherwise known as the Axiom of Extensionality or Axiom of Extent.