Changes for clojure.set/difference

jafingerhut on Wed, 28 Mar 2012
user=> (difference #{1 2 3})
#{1 2 3}
user=> (difference #{1 2} #{2 3})
#{1}
user=> (difference #{1 2 3} #{1} #{1 4} #{3})
#{2}
Brian Marick on Sat, 10 Jul 2010
user=> (difference #{1 2 3})
#{1 2 3}
user=> (difference #{1 2} #{2 3})
#{1}
user=> (difference #{1 2 3} #{1} #{1 4} #{3})
#{2}