anchor.diff:  CLOUD and add MULTIPLIER times the cloud statistics of [persistent]
   contrastive divergence."))
   
  -(defun hijack-means-to-activation (chunks clouds &key addp)
  +(defun hijack-means-to-activation (chunks clouds)
     "Set NODES of CHUNKS to the activations calculated from CLOUDS. Skip
   chunks that don't need activations. If ADDP don't zero NODES first,
   but add to it."
     ;; Zero activations or copy cached activations coming from
     ;; conditioning chunks.
  -  (unless addp
  -    (dolist (chunk chunks)
  -      (unless (conditioning-chunk-p chunk)
  -        (zero-chunk chunk))))
  +  (dolist (chunk chunks)
  +    (unless (conditioning-chunk-p chunk)
  +      (zero-chunk chunk)))
     (dolist (cloud clouds)
       (when (and (member (chunk2 cloud) chunks)
                  (not (conditioning-chunk-p (chunk2 cloud))))
  
positive.code:         on (rest (clouds-up-to-layers dbm))
          while layer
          do (swap-nodes layer-below)
          ;; This is an alternative implementation that doubles the
          ;; biases from below.
          #+nil
          (let* ((layer*
                  (set-difference layer (visible-and-conditioning-chunks dbm)))
                 (layer-above*
  
negative.code:           (dolist (chunk layer*)
              (when (connects-to-p chunk layer-above* clouds-up-to-layer-above)
                (matlisp:scal! #.(flt 2) (nodes chunk))))
            (map nil #'set-chunk-mean layer*)
            (swap-nodes layer-below))))
  
  