anchor.diff:               alist
                :key key))
   
  -(declaim (inline set-difference union intersection set-exclusive-or))
  +(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))
  
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:         (t
           list-1)))
  
  (defun nset-difference (list-1 list-2 &key key test test-not)
    (set-difference list-1 list-2 :key key :test test :test-not test-not))
  
  (defun union (list-1 list-2 &key key test test-not)
    (when (not key)
      (setf key 'identity))
  