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(use-modules (srfi srfi-1)
(srfi srfi-42))
(define (square x)
(* x x))
;; Euclid's formula.
(define (make-triple n m)
(list (- (square n) (square m))
(* 2 n m)
(+ (square n) (square m))))
(define (generate-triples max-n)
(concatenate
(list-ec (:range n 2 max-n)
(list-ec (:range m 1 (1- n))
(make-triple n m)))))
(define (find-triple-sum goal)
(find (lambda (triple)
(= (apply + triple) goal))
;; Assumed that a range of 50 would be enough.
(generate-triples 50)))
(apply * (find-triple-sum 1000))
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