anchor.diff:         (mgl-bm::sparsity-gradient-sources trainer)))
    
  -(defun dbn-mean-field-errors
  +
  +(defun dbn-mean-field-errors*
       (sampler dbn &key (rbm (last1 (rbms dbn)))
        (counters-and-measurers
         (make-dbn-reconstruction-rmse-counters-and-measurers dbn :rbm rbm)))
  
positive.code:     (values (get-error counter)
              (get-error ce-counter))))
  
  (defun make-bpn (bm defs chunk-name)
    (let ((bpn (eval (print
                      `(build-bpn (:class 'mnist-bpn :max-n-stripes 1000)
                         ,@defs
  
negative.code:              (when counters-and-measurers
                 (let ((errors (map 'list
                                    #'get-error
                                    (dbn-mean-field-errors*
                                     (make-sampler (subseq *training-images* 0 10000)
                                                   :max-n
                                                   10000
  