Set_Operators

 A set operator forms the  union,  intersection,  difference,  or
 exclusive-OR of two sets, compares two sets, or tests an ordinal
 value for inclusion in a set.  Its result is either a set  or  a
 Boolean value.

 Set Operators:

      operator  |  example  |    result
      --------------------------------------------
         +         A + B      Set that is the union of sets A and B
         *         A * B      Set that is the intersection of sets A
                              and B
         -         A - B      Set of those elements in set A that are
                              not also in set B
         =         A = B      TRUE if set A is equal to set B
         <>        A <> B     TRUE if set A is not equal to set B
         <=        A <= B     TRUE if set A is a subset of set B
         >=        A >= B     TRUE if set B is a subset of set A
         IN        C IN B     TRUE if C is an element of set B
         NOT IN    C NOT IN B TRUE if C is not an element of B