anchor.diff:          (list-1)
           (list-2)))
   
  +(defun nunion (list-1 list-2 &key key test test-not)
  +  (union list-1 list-2 :key key :test test :test-not test-not))
  +
   (defun intersection (list-1 list-2 &key key test test-not)
     (when (not key)
       (setf key 'identity))
  
positive.code:         (t
           list-1)))
  
  (defun union (list-1 list-2 &key key test test-not)
    (when (not key)
      (setf key 'identity))
  
negative.code:       (when (not (member (funcall key e) list-1 :key key :test test :test-not test-not))
          (push e result)))
      result))
  
  (defun nset-exclusive-or (list-1 list-2 &key key test test-not)
    (set-exclusive-or list-1 list-2 :key key :test test :test-not test-not))
  
  (defun subsetp (list-1 list-2 &key key test test-not)
    (when (not key)
  