This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
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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
Intersection[list1,list2,...]give a list of the elements that are common to all the
Complement[universal,list1,...]give a list of the elements that are in universal, but not in any of the
Subsets[list]give a list of all subsets of the elements in list
DeleteDuplicates[list]delete all duplicates from list

Set theoretical functions.

Union gives the elements that occur in any of the lists.
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Intersection gives only elements that occur in all the lists.
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Complement gives elements that occur in the first list, but not in any of the others.
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This gives all the subsets of the list.
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DeleteDuplicates deletes all duplicate elements from the list.
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