Great-Circle-Distance implement

(defun great-circle-distance (from-longitude from-latitude to-longitude to-latitude)
  (let ((Earth-radius 6371))
       (* 2
          Earth-radius
          (asin (min (sqrt (* (expt (sin (/ (- to-latitude  from-latitude ) 2)) 2)
                              (expt (sin (/ (- to-longitude from-longitude) 2)) 2)
                              (cos to-latitude)))
                 1)))))

(defun transport-time (distance)
  (flet ((format-and-print (divisor transport-method)
           (format NIL "Human terms: ~a away by ~a, using an average speed of ~a km/h."
                   (/ distance divisor) transport-method divisor)))
    (cond
     ((< distance 0))
     ((< distance 150)
      (format-and-print 50 "car"))
     ((< distance 2500)
      (format-and-print 130 "train"))
     ((< distance 12500)
      (format-and-print 800 "plane"))
     (T
      (format-and-print 18000 "ICBM")))))

(multiple-value-bind (from-latitude from-longitude) (coordinates place1)
  (multiple-value-bind (to-latitude to-longitude) (coordinates place2)
    (let ((distance) (great-circle-distance from-longitude from-latitude to-longitude to-latitude))
         (format NIL "Distance: ~a km" distance)
         (transport-time distance))))