import ordset.

go =>
  A = ["John", "Serena", "Bob", "Mary", "Serena"].new_ordset(),
  B = ["Jim", "Mary", "John", "Jim", "Bob"].new_ordset(),

  println(symmetric_difference=symmetric_difference(A,B)),
  println(symmetric_difference2=symmetric_difference2(A,B)),

  println(subtractAB=subtract(A,B)),
  println(subtractBA=subtract(B,A)),

  println(union=union(A,B)),
  println(intersection=intersection(A,B)),
  nl.

symmetric_difference(A,B) = union(subtract(A,B), subtract(B,A)).
% variant
symmetric_difference2(A,B) = subtract(union(A,B), intersection(B,A)).