anchor.diff:     (design2 :initarg :design2
               :type design)))
   
  -(defvar +flipping-ink+ (load-time-value   (make-instance 'standard-flipping-ink 
  -                                            :design1 +foreground-ink+
  -                                            :design2 +background-ink+)))
  +(defvar +flipping-ink+ (make-instance 'standard-flipping-ink 
  +                         :design1 +foreground-ink+
  +                         :design2 +background-ink+))
   
   (defmethod print-object ((ink (eql +flipping-ink+)) stream)
     (format stream "#.~S" '+flipping-ink+))
  
positive.code:          (make-instance 'standard-opacity :value value))))
  
  (defvar +transparent-ink+ 
      (load-time-value (make-instance 'standard-opacity :value 0)))
  
  ;;;;
  ;;;; 13.6 Indirect Inks
  
negative.code: 
  (defclass indirect-ink (design) ())
  
  (defvar +foreground-ink+ (make-instance 'indirect-ink))
  (defvar +background-ink+ (make-instance 'indirect-ink))
  
  (defmethod print-object ((ink (eql +foreground-ink+)) stream)
    (format stream "#.~S" '+foreground-ink+))
  