1 (defun make-rat (n d)
2   (labels ((make-rat-reduce (n d)
3 	     (let ((g (gcd n d)))
4 	       (cons (/ n g) (/ d g)))))
5     (cond ((and (< n 0) (< d 0))
6 	   (make-rat-reduce (- n) (- d)))
7 	  ((and (< d 0) (> n 0))
8 	   (make-rat-reduce (- n) (- d)))
9 	  (t (make-rat-reduce n d)))))
10 (defun numer (x)
11   (car x))
12 (defun denom (x)
13   (cdr x))
14