clojure-koans/05_sets.clj

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

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

  ; "Remember that a set is a *mathematical* set"
  (= #{1 2 3 4 5} (set '(1 1 2 2 3 3 4 4 5 5))) ;; J - This creates a unique ORDERED set so it's always sorted.

  ; "You can ask clojure for the union of two sets"
  (= #{1 2 3 4 5} (set/union #{1 2 3 4} #{2 3 5})) ;; J - Uniting sets still orders them and keeps elements unique

  ; "And also the intersection"
  (= #{2 3} (set/intersection #{1 2 3 4} #{2 3 5})) ;; J - Creates a new set of common elements.

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