anchor.diff:  (defmethod get-neuron ((net t-net) (layer-index integer) (neuron-index integer))
     (elt (neuron-array (elt (layers net) layer-index)) neuron-index))
   
  +(defun set-layer-transfer-function (net layer-index transfer-tag)
  +  (loop for neuron across (neuron-array (elt (layers net) layer-index))
  +     do (setf (transfer-tag neuron) transfer-tag)
  +       (setf (transfer-function neuron)
  +             (transfer-functions transfer-tag :function))
  +       (setf (transfer-derivative neuron)
  +             (transfer-functions transfer-tag :derivative))))
  +
  +(defun set-network-transfer-function (net transfer-tag)
  +  (loop for layer in (layers net) do
  +       (set-layer-transfer-function net (layer-index layer) transfer-tag)))
  +
   (defmethod transfer ((neuron t-neuron))
     (setf (output neuron)
           (funcall (transfer-function neuron) (input neuron)))
  
positive.code:               :layer-index layer-index
                :layer-type
                (cond ((zerop layer-index) :input)
                      ((= layer-index (1- (length (topology net)))) :output)
                      (t :hidden))
                :neuron-count (elt (topology net) layer-index)
                :transfer-tag (transfer-tag net)
                ;; (if (= layer-index (1- (length (topology net))))
                ;;     :logistic
                ;;     (transfer-tag net))
                :net net)))
    (loop for layer in (layers net)
       for next-layer = (if (eql (layer-type layer) :output)
  
negative.code: 
  (defmethod initialize-instance :after ((net t-net) &key)
    (setf (layers net)
          (loop with output-layer-index = (1- (length (topology net)))
             for layer-spec in (topology net)
             for layer-index = 0 then (1+ layer-index)
             collect
               (make-instance
  