anchor.diff:     #'maybe-prune
      (sort (loop for buffer in potentially-superfluous-buffers
                  when (find-prune buffer) collect it)
  -         #'> :key #'prune-size)))
  +         #'> :key #'prune-bits)))
   
   (defvar *prune*)
   
  
positive.code:         ;; obsolete by the prune, and where the corresponding value is a
          ;; list of all dendrites that have reached that buffer.
          (buffer-dendrites-alist (collect-prune-buffer-dendrites-alist buffer))
          ;; The sum of the number of elements of all the buffers that are
          ;; rendered obsolete by this prune.
          (size 0))
      (when (null buffer-dendrites-alist)
        (return-from find-prune nil))
      ;; Ensure that each dendrite has a unique associated writer.
      (loop for (buffer . dendrites) in buffer-dendrites-alist do
        (incf size (buffer-size buffer))
        (loop for dendrite in dendrites do
          (assert (eq buffer (load-instruction-buffer (cdr (dendrite-cons dendrite)))))
          (block check-one-dendrite
  
negative.code:           ;; writer for this particular dendrite.  Give up.
            (return-from find-prune nil))))
      (make-prune
       :bits bits
       :buffers
       ;; Mark each buffer that is part of a prune as superfluous.
       (mapcar #'car buffer-dendrites-alist))))
  