jjcomer

(use '[clojure.set :only (difference union intersection)])

(defn without
  "Returns set s with x removed."
  [s x] (disj s x))

(defn take-1
  "Returns the pair [element, s'] where s' is set s with element removed."
  [s] {:pre [(not (empty? s))]}
  (let [item (first s)]