anchor.diff:          (setf (car (cdr x)) new-value)
           (return-from body new-value)))
       (mop-push-on-end key plist)
  -    (mop-push-on-end new-value plit)
  +    (mop-push-on-end new-value plist)
       new-value))
   
   (defun mop-mapappend (fun &rest args)
  
positive.code: ; PERFORMANCE OF THIS SOFTWARE.
  
  ;-------------------------------------------------------------------------------
  ; Behavior/support/utility layer.
  ;-------------------------------------------------------------------------------
  
  (defmacro mop-push-on-end (value location)
  
negative.code:     (:metaclass (list ':metaclass `(find-class ',(cadr option))))
      (:default-initargs (list ':direct-default-initargs
                               `(list ,@(mop-mapappend #'(lambda (x) x)
                                                    (mop-mapplist #'(lambda (key value)
                                                                      `(',key ,value))
                                                                  (cdr option))))))
      (otherwise (list `',(car option) `',(cadr option)))))
  
  (defun mop-canonicalize-defclass-options (options)
    (mop-mapappend #'mop-canonicalize-defclass-option options))
  
  (defun mop-ensure-class (name &rest all-keys)
    (if (mop-find-class name nil)
  