anchor.diff:     #+nil
      (noisyp :initform nil :initarg :noisyp :accessor noisyp))
     (:documentation "max(0,x) activation function. If NOISYP then add
  -normal(0,sigmoid(x)) noise to x."))
  +  normal(0,sigmoid(x)) noise to x."))
   
   (defmethod default-size ((lump ->rectified))
     (size (x lump)))
  
positive.code: 
  (defun first-trained-weight-lump (trainer learner)
    "Much time can be wasted computing derivatives of non-trained weight
  lumps. Return the first one that TRAINER trains."
    (or (slot-value learner 'first-trained-lump)
        (setf (slot-value learner 'first-trained-lump)
              (find-if (lambda (lump)
  
negative.code: 
  (defmethod cost (bpn)
    "Return the sum of costs for all active stripes. The cost of a
    stripe is the sum of the error nodes. The second value is the number
    of stripes."
    (let ((sum (flt 0)))
      (loop for lump across (lumps bpn) do
        (when (typep lump '->error)
  