(define x (list 1 2 3 4 5 6 7))
(define y (list 8 9 10 11 12 13))
(define z (list 14 15 16 17 18 19 20))
(define (flatmap proc seq)
(foldr append '() (map proc seq)))
(display (flatmap append (list x y z)))
(newline)
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