anchor.diff:    ;; 4, 5, 6, 7, 8 and 9?
     (-<> "0123456789"
       (gathering-vector (:size (factorial (length <>)))
  -      (map-permutations #'gather <>))
  -    (map-into <> #'parse-integer <>)
  +      (map-permutations (compose #'gather #'parse-integer) <>
  +                        :copy nil))
       (sort <> #'<)
       (elt <> (1- 1000000))))
   
  
positive.code:       ((null coins) 0)
        (t (+ (recur (- amount (first coins)) coins)
              (recur amount (rest coins)))))))
  
  
  ;;;; Tests --------------------------------------------------------------------
  
negative.code: (test p29 (is (= 9183 (problem-29))))
  (test p30 (is (= 443839 (problem-30))))
  (test p31 (is (= 73682 (problem-31))))
  (test p32 (is (= 45228 (problem-32))))
  (test p33 (is (= 100 (problem-33))))
  
  
  ;; (run! :euler)
  