anchor.diff:  ;; ---------------------------------------------------------------------------------------------------------------------
   ;; types
   ;; ---------------------------------------------------------------------------------------------------------------------
  -
  -(defclass red-black-node ()
  -  ((parent :initform nil :accessor parent)
  -   (left :initform nil :accessor left)
  -   (right :initform nil :accessor right)
  -   (color :initform nil :accessor color)
  -   (key :initform nil :initarg :key :accessor key)
  -   (data :initform nil :initarg :data :accessor data)))
  -
  -(defclass red-black-tree ()
  -  ((root :accessor root)
  -   (leaf :accessor leaf)))
   
   ;; ---------------------------------------------------------------------------------------------------------------------
   ;; generics
  
positive.code: ;; ---------------------------------------------------------------------------------------------------------------------
  
  ;; Nodes
  
  (macrolet 
      ((define-slot (name)
  
negative.code: 
  ;; Trees
  
  (defclass red-black-tree () ())
  
  (defgeneric root (tree))
  (defgeneric (setf root) (value tree))
  
  