Changes for clojure.set/intersection

zkim on Sun, 26 Sep 2010
user=> (intersection #{1})
#{1}
user=> (intersection #{1 2} #{2 3})
#{2}
user=> (intersection #{1 2} #{2 3} #{3 4})
#{}
user=> (intersection #{1 :a} #{:a 3} #{:a})
#{:a}
Brian Marick on Mon, 12 Jul 2010
(intersection #{1}) => #{1}
(intersection #{1 2} #{2 3}) => #{2}
(intersection #{1 2} #{2 3} #{3 4}) => #{}
(intersection #{1 :a} #{:a 3} #{:a}) => #{:a}