anchor.diff:  
   (defun make-rectangular-tile (design width height)
     (make-instance 'rectangular-tile
  -    :width width
  +    :width  width
       :height height
       :design design))
   
  -
   ;;;
   
   (defclass in-compositum (design)
  -  ((ink :initarg :ink :reader compositum-ink)
  +  ((ink  :initarg :ink  :reader compositum-ink)
      (mask :initarg :mask :reader compositum-mask)))
   
   (defmethod print-object ((object in-compositum) stream)
  
positive.code:          (x (* +ihs-rgb-c1+ s3 cos-hh intensity))
           (y (* +ihs-rgb-c2+ s3 sin-hh intensity))
           (z (* +ihs-rgb-c3+ c3 intensity)))
      (values (max 0 (min 1 (+ x x z)))
              (max 0 (min 1 (+ y z (- x))))
              (max 0 (min 1 (- z x y))))))
  
negative.code:         (t
           (make-instance 'standard-opacity :value value))))
  
  ;;;;
  ;;;; 13.7 Flipping Ink
  ;;;;
  