lisp test

(defn union
  "Return a set that is the union of the input sets"
  ([] #{})
  ([s1] s1)
  ([s1 s2]
     (if (< (count s1) (count s2))
       (reduce conj s2 s1)
       (reduce conj s1 s2)))
  ([s1 s2 & sets]
     (let [bubbled-sets (bubble-max-key count (conj sets s2 s1))]
       (reduce into (first bubbled-sets) (rest bubbled-sets)))))

(defn intersection
  "Return a set that is the intersection of the input sets"
  ([s1] s1)
  ([s1 s2]
     (if (< (count s2) (count s1))
       (recur s2 s1)
       (reduce (fn [result item]
                   (if (contains? s2 item)
		     result
                     (disj result item)))
	       s1 s1)))
  ([s1 s2 & sets] 
     (let [bubbled-sets (bubble-max-key #(- (count %)) (conj sets s2 s1))]
       (reduce intersection (first bubbled-sets) (rest bubbled-sets)))))