clojure-koans/05_sets.clj

  ; "You can create a set by converting another collection"
  (= #{3} (set __))

  ; "Counting them is like counting other collections"
  (= __ (count #{1 2 3}))

  ; "Remember that a set is a *mathematical* set"
  (= __ (set '(1 1 2 2 3 3 4 4 5 5)))

  ; "You can ask clojure for the union of two sets"
  (= __ (set/union #{1 2 3 4} #{2 3 5}))

  ; "And also the intersection"
  (= __ (set/intersection #{1 2 3 4} #{2 3 5}))

  ; "But don't forget about the difference"
  (= __ (set/difference #{1 2 3 4 5} #{2 3 5}))