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