anchor.diff:                          (if (> part-count 3) 1 day)
                           (if (> part-count 4) 1 month)
                           year
  -                        :offset offset
                           :timezone timezone
                           :into into))))
   
  
positive.code:                           (if (> part-count 3) (days-in-month month year) day)
                            month
                            year
                            :offset offset
                            :timezone timezone
                            :into into)))))
  
  
negative.code:             timestamp-parts)
      (multiple-value-bind (nsec sec min hour day month year day-of-week daylight-saving-time-p offset)
          (decode-timestamp timestamp :timezone timezone)
        (declare (ignore nsec day-of-week daylight-saving-time-p offset))
        (encode-timestamp 0
                          (if (> part-count 0) 0 sec)
                          (if (> part-count 1) 0 min)
  