anchor.diff:          (t
            (make-instance 'standard-opacity :value value))))
   
  -(defvar +transparent-ink+ 
  -    (make-instance 'standard-opacity :value 0))
  -
  -;;;;
  -;;;; 13.6 Indirect Inks
  -;;;;
  -
  -(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+))
  -
  -(defmethod print-object ((ink (eql +background-ink+)) stream)
  -  (format stream "#.~S" '+background-ink+))
  -
   ;;;;
   ;;;; 13.7 Flipping Ink
   ;;;;
  
positive.code: ;; (make-opacity 1) = +foreground-ink+ = +everywhere+
  ;;
  ;; --GB
  
  ;;;; What we may want to have
  
  ;; It might be handy to have the equivalent of parent-relative
  ;; backgrounds. We can specify new indirect inks:
  
negative.code: ||#
  
  ;;;;
  ;;;; 13.6 Indirect Inks
  ;;;;
  
  (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+))
  
  (defmethod print-object ((ink (eql +background-ink+)) stream)
    (format stream "#.~S" '+background-ink+))
  
  ;;;;
  ;;;; 13.4 Opacity
  ;;;;
  
  