anchor.diff:  (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)
  
positive.code:       ((null coins) 0)
        (t (+ (recur (- amount (first coins)) coins)
              (recur amount (rest coins)))))))
  
  
  ;;;; Tests --------------------------------------------------------------------
  
negative.code:   ;; 4, 5, 6, 7, 8 and 9?
    (-<> "0123456789"
      (gathering-vector (:size (factorial (length <>)))
        (map-permutations (compose #'gather #'parse-integer) <>
                          :copy nil))
      (sort <> #'<)
      (elt <> (1- 1000000))))
  
  