anchor.diff:  of chunks. The layers partition the set of all chunks in the BM.
   Chunks with no connections to layers below are visible (including
   constant and conditioning) chunks. The layered structure is used in
  -the single, bottom-up approximate inference pass. When instantiating a
  -DBM, VISIBLE-CHUNKS and HIDDEN-CHUNKS are inferred from LAYERS and
  +the single, bottom-up, approximate inference pass. When instantiating
  +a DBM, VISIBLE-CHUNKS and HIDDEN-CHUNKS are inferred from LAYERS and
   CLOUDS.")
      (clouds-up-to-layers
       :type list :reader clouds-up-to-layers
  
positive.code:                                      (n-undamped-iterations 100)
                                       (n-damped-iterations 100)
                                       (damping-factor #.(flt 0.9)))
    "A supervisor for SETTLE-MEAN-FIELD. Return NIL if average of the
  absolute value of change in nodes is below NODE-CHANGE-LIMIT, else
  return 0 damping for N-UNDAMPED-ITERATIONS then DAMPING-FACTOR for
  another N-DAMPED-ITERATIONS, then NIL."
    (declare (ignore bm))
  
negative.code:     :documentation "A BM that keeps the states of the persistent
  chains (each stripe is a chain), initialized from the BM being trained
  by COPY with 'PCD as the context. Suitable for training BM and
  RBM."))
    (:documentation "Persistent Contrastive Divergence trainer."))
  
  (defmethod initialize-trainer ((trainer bm-pcd-trainer) (bm bm))
    (setf (slot-value trainer 'normal-chains) bm)
  