The set of elements belonging to one but not both of two given sets. It is therefore the union of the complement
 of 
 with respect to 
 and 
 with respect to 
,
 and corresponds to the XOR operation in Boolean logic. The
 symmetric difference can be implemented in the Wolfram
 Language as:
  SymmetricDifference[a_, b_] :=
    Union[Complement[a, b], Complement[b, a]]
The symmetric difference of sets  and 
 is variously written as 
, 
, 
 (Borowski and Borwein 1991) or 
 (Harris and Stocker 1998, p. 3). All but the first
 notation should probably be deprecated since each of the other symbols has a common
 meaning in other areas of mathematics.
For example, for 
 and 
,
 
,
 since 2, 3, and 5 are each in one, but not both, sets.