; -------------------------------- The gcd function in LISP. 
(defun gcd(x y) 
  (cond (
    (or (< x 0) (< y 0)) (gcd (abs x) (abs y)) ) 
    ((< x y)             (gcd y x)           ) 
    ((= y 0)             x                   ) 
    (                    (gcd y (rem x y))   ) )) 

; --------------------------------------------- Calling gcd 
(defun gcdprint(a b) 
  (let ( 
       (f (list "The gcd of " a " and " b " is " (gcd a b))) 
       ) 
       (mapcar ’princ f) 
       (terpri)               ))