Quicksort in Clojure

quicksort.clj

(defn pivot-and-rest [coll]
  (let [splitted (split-at (quot (count coll) 2) coll)
        second-part (second splitted)]
    [(first second-part) (concat (first splitted) (rest second-part))]))

(defn quicksort [coll]
  (cond
    (empty? coll) []
    (= (count coll) 1) coll
    :else (let [[p xs] (pivot-and-rest coll)
                {lesser true greater false} (group-by #(< % p) xs)]
      (concat (quicksort lesser) [p] (quicksort greater)))
  ))

(assert (= (quicksort []) []))
(assert (= (quicksort [1]) [1]))
(assert (= (quicksort [2 1 3]) [1 2 3]))
(assert (= (quicksort [2 1 4 3]) [1 2 3 4]))