permutations.clj

(defn rotations [xs] 
  (take (count xs) (partition (count xs) 1 (cycle xs))))

(defn permutations [a-set]
  (if (empty? a-set)
    (list)
    (mapcat
     (fn [[x & xs]] (map #(cons x %) (permutations xs)))
     (rotations a-set))))

;; based on https://codereview.stackexchange.com/questions/135737/generate-all-permutations-in-clojure