Editing Naive set theory (section)

=== Equality ===
Two sets ''A'' and ''B'' are defined to be '''[[Equality (mathematics)|equal]]''' when they have precisely the same elements, that is, if every element of ''A'' is an element of ''B'' and every element of ''B'' is an element of ''A''. (See [[axiom of extensionality]].) Thus a set is completely determined by its elements; the description is immaterial. For example, the set with elements 2, 3, and 5 is equal to the set of all [[prime number]]s less than 6.
If the sets ''A'' and ''B'' are equal, this is denoted symbolically as ''A''&nbsp;=&nbsp;''B'' (as usual).