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'''Set theory''' a branch of [[mathematics]] dealing with collections of objects.   

'''Set theory''' is a branch of [[mathematics]] dealing with collections of objects.   

*The language of set theory is based on a single fundamental relation, called membership. We say that A is a member of B (in symbols A  ∈ B), or that the set B contains A as its element. The understanding is that a set is determined by its elements; in other words, two sets are deemed equal if they have exactly the same elements. <ref>http://plato.stanford.edu/entries/set-theory/</ref>

*The language of set theory is based on a single fundamental relation, called membership. We say that A is a member of B (in symbols A  ∈ B), or that the set B contains A as its element. The understanding is that a set is determined by its elements; in other words, two sets are deemed equal if they have exactly the same elements. <ref>http://plato.stanford.edu/entries/set-theory/</ref>