This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
 Mathematica Tutorial Functions »|Tutorials »

# Lists as Sets

Mathematica usually keeps the elements of a list in exactly the order you originally entered them. If you want to treat a Mathematica list like a mathematical set, however, you may want to ignore the order of elements in the list.
 Union[list1,list2,...] give a list of the distinct elements in the listi Intersection[list1,list2,...] give a list of the elements that are common to all the listi Complement[universal,list1,...] give a list of the elements that are in universal, but not in any of the listi Subsets[list] give a list of all subsets of the elements in list

Set theoretical functions.

Union gives the elements that occur in any of the lists.
 Out[1]=
Intersection gives only elements that occur in all the lists.
 Out[2]=
Complement gives elements that occur in the first list, but not in any of the others.
 Out[3]=
This gives all the subsets of the list.
 Out[4]=