Determine the prime factors of a given positive integer

	;; P35 (**) Determine the prime factors of a given positive integer.
	;; Construct a flat list containing the prime factors in ascending order.
	;; Example:
	;; * (prime-factors 315)
	;; (3 3 5 7)
	#lang racket
	(provide prime-factors)
	(require "p31.ss")
	(define (prime-factors n)
	(let loop ((x n) (y 2) (acc '()))
	(cond
	((= x 1)
	(reverse acc))
	((and (is-prime? y) (zero? (modulo x y)))
	(loop (/ x y) 2 (cons y acc)))
	(else
	(loop x (+ y 1) acc)))))

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