anchor.diff:  (defparameter +astronomical-julian-date-offset+ -2451605)
   
   ;; The modified julian date is the number of days between the current
  -;; date and 1858-11-17T12:00:00+00:00.  For the sake of simplicity,
  +;; date and 1858-11-17T12:00:00+00:00. TODO: For the sake of simplicity,
   ;; we currently just do the date arithmetic and don't adjust for the
   ;; time of day.
   (defparameter +modified-julian-date-offset+ -51604)
  
positive.code:       (error "~S is not a valid date string" string))
      date))
  
  (defun format-rfc3339-timestring (local-time &key omit-date-part-p omit-time-part-p
                                    omit-timezone-part-p (use-zulu-p t))
    (format-timestring local-time :omit-date-part-p omit-date-part-p :omit-time-part-p omit-time-part-p
                       :omit-timezone-part-p omit-timezone-part-p :use-zulu-p use-zulu-p))
  
  (defun format-timestring (local-time &key destination timezone (omit-date-part-p nil)
  
negative.code:            (encode-local-time-into-values nsec sec minute hour day month year :timezone timezone))))))
  
  (defun %offset-local-time-part (time part offset)
    "Returns a time adjusted by the specified OFFSET. Takes care of different kinds of overflows. The setting :day-of-week is possible using a keyword symbol name of a week-day (see +DAY-NAMES-AS-KEYWORDS+) as value. In that case point the result to the previous day given by OFFSET."
    (labels ((direct-adjust (part offset nsec sec day timezone)
               (cond ((eq part :day-of-week)
                      (with-decoded-local-time (:day-of-week day-of-week)
  