Clojure Merge Sort using lazy-seq and partition-all

mergesort.clj

(defn merge-sorted
  "Merge two sorted sequences into one sorted sequence
  If called with one sequence as argument, return the sequence unchanged"
  ([xs] xs)
  ([[head1 & tail1 :as xs1] [head2 & tail2 :as xs2]]
   (cond
     (some empty? [xs1 xs2])
     (concat xs1 xs2)
     
     (< head1 head2)
     (lazy-seq (cons head1 (merge-sorted tail1 xs2)))
     
     :else
     (lazy-seq (cons head2 (merge-sorted xs1 tail2))))))


(defn merge-sort 
  "Sort sequence using tail-recursive application of merge"
  [xs]
  (loop [list-seq (map list xs)]
    (if (empty? (rest list-seq))
      (first list-seq)
      (recur (map #(apply merge-sorted %) (partition-all 2 list-seq))))))