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Exercise solution:
The cartesian product of two sets

Here follows two slightly different solutions. The first without reduce.

 
(define (cartesian-product set-list-1 set-list-2)
  (apply
     append
     (map (lambda (b)
            (map (lambda (a) (cons a b)) set-list-1))
          set-list-2)))

(define (cartesian-product set-list-1 set-list-2)
  (reduce-right
      append
      (map (lambda (b)
            (map (lambda (a) (cons a b)) set-list-1))
          set-list-2)))

(define (reduce-right f lst)
  (if (null? (cdr lst))
      (car lst)
      (f (car lst) 
         (reduce-right f (cdr lst)))))

The first solution comes from Christian Wagenknecht's book 'Programmierparadigmen', from Springer Verlag.