anchor.diff:  
   (defun update-lm (lm input)
     (declare (optimize speed (safety 1) (debug 0)))
  +  #+ () (prog1 lm
  +          (dolist (token (tokens input))
  +            (map-ngrams
  +             (lambda (word start end)
  +               (let ((ngram (subseq word start end)))
  +                 (incf (gethash ngram lm 0))))
  +             token)))
  +  ;; NB This version is optimized to allocate as little as possible.
  +  ;; To do the hashing, we re-use a displaced array as a window across
  +  ;; all tokens. Only if there is no entry for an ngram do we allocate
  +  ;; a new, also displaced array to serve as the key. No strings are
  +  ;; allocated for ngrams.
     (prog1 lm
       (let ((window (make-array 0 :adjustable t :displaced-to "" :element-type 'character)))
         (dolist (token (tokens input))
           (map-ngrams
  -         #+ () (let ((ngram (subseq word start end)))
  -                 (incf (gethash ngram lm 0)))
  -         ;; NB This version is optimized to allocate as little as
  -         ;; possible. To do the hashing, we re-use `window' from
  -         ;; above. Only if there is no entry for an ngram do we
  -         ;; allocate a new displaced array to serve as the key. No
  -         ;; strings are allocated for ngrams.
            (lambda (word start end)
              (declare (string word) (array-index start end))
              (let ((ngram
  
positive.code:                                  :displaced-index-offset start)))
               (multiple-value-bind (count there?)
                   (gethash ngram lm 0)
                 (declare (array-index count))
                 (let ((key (if there? ngram (nsubseq word start end))))
                   (setf (gethash key lm) (1+ count))))))
           token)))))
  
negative.code:     (map-into model #'car model)))
  
  (defun language-score (unknown model &optional (ngram-limit *ngram-limit*))
    (declare (optimize speed (debug 0) (safety 1)))
    (loop for i of-type array-index from 0
          for ngram in unknown
          for match = (gethash ngram model)
          if match
  