(defun equal-frequency-discretization (data n &optional (cautions (make-caution)))
  (let* ((numbers (sane-numbers data cautions))
         (want    (round (/ (length numbers) n)))
         (break-at (breaks numbers want))
         (new      (mapcar #'(lambda(datum)
                               (efd1 datum break-at))
                           data)))
        new))

(defun efd1 (x break-at)
  (if (unknownp x)
      x
      (dolist (b break-at b)
        (if (<= x b ) (return-from efd1 b)))))

(defun breaks (l max-size)
  (let (out)
   (reverse
    (breaks1 (first l) (rest l) nil out 1 max-size))))

(defun breaks1 (x l b4 out n max-size)
  (unless (eql x b4)
    (when (>= n max-size)
      (setf n 0)
      (push x out)))
  (cond (l  (breaks1 (first l) (rest l) x out (1+ n) max-size))
        (t  (pushnew x out)
            out)))