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Task/Symmetric-difference/00DESCRIPTION

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+Given two [[set]]s ''A'' and ''B'', where ''A'' contains:
+
+* John
+* Bob
+* Mary
+* Serena
+
+and ''B'' contains:
+
+* Jim
+* Mary
+* John
+* Bob
+
+compute
+
+:<math>(A \setminus B) \cup (B \setminus A).</math>
+
+That is, enumerate the items that are in ''A'' or ''B'' but not both. This set is called the [[wp:Symmetric difference|symmetric difference]] of ''A'' and ''B''.
+
+In other words: <math>(A \cup B) \setminus (A \cap B)</math> (the set of items that are in at least one of ''A'' or ''B'' minus the set of items that are in both ''A'' and ''B'').
+
+Optionally, give the individual differences (<math>A \setminus B</math> and <math>B \setminus A</math>) as well.
+
+;Notes
+# If your code uses lists of items to represent sets then ensure duplicate items in lists are correctly handled. For example two lists representing sets of <code>a = ["John", "Serena", "Bob", "Mary", "Serena"]</code> and <code>b = ["Jim", "Mary", "John", "Jim", "Bob"]</code> should produce the result of just two strings: <code>["Serena", "Jim"]</code>, in any order.
+# In the mathematical notation above <code>A \ B</code> gives the set of items in A that are not in B; <code>A ∪ B</code> gives the set of items in both A and B, (their ''union''); and <code>A ∩ B</code> gives the set of items that are in both A and B (their ''intersection'').