gistfile1.clj

(defn powerset [list]
     (if (empty? list) [list]
        (let [[hd & tl] list ptl (powerset tl)]
	  (lazy-cat (map #(conj % hd) ptl) ptl))))

(defn set-powerset [a-seq]
     (if (empty? a-seq) #{#{}}
        (let [hd (first a-seq) 
	      tl (rest a-seq) 
	      ptl (set-powerset tl)]
	  (clojure.set/union ptl (map #(conj % hd) ptl)))))