;; (import (chicken string))
;; (import (chicken format))
(define (tally eq? xs)
  (define (aux acc xs)
    (if (null? xs)
        acc
        (let* ((k (car xs))
               (v (alist-ref k acc eq?))
               (a (alist-update k (+ 1 (or v 0)) acc eq?)))
          (aux a (cdr xs)))))
  (aux '() xs))
(define (filter f xs)
  (reverse (foldl (lambda (acc x) (if (f x) (cons x acc) acc)) '() xs)))
(define f
  (compose
   (cut apply string-append <>)
   (cut map car <>)
   (cut filter (lambda (kv) (< 1 (cdr kv))) <>)
   (cut tally equal? <>)
   (cut string-chop <> 1)))
(define (g s)
  (format #t "~A -> ~A~%" s (f s)))
(g "T")
(g "CG")
(g "ATA")
(g "CGGA")
(g "ATGAT")
(g "GTTGCA")
(g "CCCCGGG")
(g "ACTGCGAG")
(g "ATCAGAATA")
(g "TGCCATGACA")
 

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