Operators 
                                +  (Set Union) 

     FUNCTION:  Set Union operator

 OPERAND TYPE:  Union

  RESULT TYPE:  Compatible set types

      REMARKS:  The result of these operations must conform to the
                rules of set logic:

          An ordinal value c is in a + b only if c is in a or b.
          An ordinal value c is in a - b only if c is in a and not in b.
          An ordinal value c is in a * b only if c is in both a and b.