anchor.diff:  by EQL to what STRIPE-LABEL-FN returns for STRIPED and the index of
   the stripe. This is a measurer function."
     (assert (= (length examples) (n-stripes striped)))
  -  (let ((sum 0))
  +  (let ((sum 0)
  +        (label-errors ()))
       (loop for example in examples
             for stripe upfrom 0
             for confidences = (funcall confidence-fn striped stripe)
  -          do (incf sum (- (log (max #.(expt 10d0 -15)
  -                                    (aref confidences
  -                                          (funcall label-fn example)))))))
  -    (values sum (length examples))))
  +          do (let* ((label (funcall label-fn example))
  +                    (err (- (log (max #.(expt 10d0 -15)
  +                                      (aref confidences label))))))
  +               (incf sum err)
  +               (let ((label-error (or (getf label-errors label)
  +                                      (setf (getf label-errors label)
  +                                            (list #.(flt 0) 0)))))
  +                 (incf (first label-error) err)
  +                 (incf (second label-error)))))
  +    (values (list sum label-errors)
  +            (length examples))))
   
   (defgeneric maybe-make-cross-entropy-measurer (obj)
     (:documentation "Return a function of one parameter that is invoked
  
positive.code:       (measure-cross-entropy examples labeled))))
  
  (defclass cross-entropy-counter (error-counter)
    ((name :initform '("cross entropy"))))
  
  
  
negative.code: 
  (defun measure-cross-entropy (examples striped
                                &key (label-fn #'label)
                                  (confidence-fn #'classification-confidences))
    "Return the sum of the cross entropy between the confidences and the
  distribution (1 at the label of the class) and the number of examples.
  The length of EXAMPLES must be equal to the number of stripes in
  