(defun equal-width-discretization (data n &optional (cautions (make-caution)))
  (let  ((numbers (sane-numbers data cautions)))
    ;(setf numbers (mapcar #'(lambda (x) (if (not (= x 0)) (log x) x)) numbers))
    (let* ((min     (first numbers))
	  (max     (first (last numbers)))
	  (width   (/ (- max min) n)))
    (labels ((datum (cell)
               (cond ((unknownp cell) cell)
                     ((numberp cell)  (discretize cell))
                     (t               *unknown*)))
               (discretize (m)
                 (float
                  (min max    ; don't blow max
                       (+ min ; convert to a number in the same range as before
                          (* width
                             (min n ; don't blow max
                                  (1+ (floor (/ (- m min) width))))))))))
      (mapcar #'datum data)))))

(defun log-continuous (data n &optional (cautions (make-caution)))
  (let ((numbers (sane-numbers data cautions)))
    ;(setf numbers (mapcar #'(lambda (x) (if (not (= x 0)) (log x) x)) numbers))
    (labels ((datum (cell)
	       (cond ((unknownp cell) cell)
		     ((numberp cell) (discretize cell))
		     (t              *unknown*)))
	     (discretize (m)
	       (if (not (= m 0)) (log m) m)))
      (mapcar #'datum data))))