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