A Venn diagram illustrating the intersection of two sets.

Set theory is the study of sets in mathematics. Sets are collections of objects. We refer to these objects as "elements" or "members" of the set. To write a set, one wraps the numbers in {curly brackets}, and separates them with commas. For example. the set \displaystyle{ \{1,2,3\} } holds 1, 2, and 3. Sets are also often referred to using capital roman letters such as \displaystyle{ A }, \displaystyle{ B }, \displaystyle{ C }.