probably the simplest way to implement dissoc-in

dissoc-in.clj

(defn dissoc-in
  [m ks]
  (let [[k & ks] ks]
    (if ks
      (let [found (find m k)]
        (if found
          (assoc m k (dissoc-in (val found) ks))
          m))
      (dissoc m k))))

;;; with vector support for terminal associative value:

(defn dissocv
  [v n]
  (vec (concat (subvec v 0 n) (subvec v (inc n)))))

(defn dissoc*
  [m k]
  (if (map? m)
    (dissoc m k)
    (dissocv m k)))

(defn dissoc-in
  [m ks]
  (let [[k & ks] ks]
    (if ks
      (let [found (find m k)]
        (if found
          (assoc m k (dissoc-in (val found) ks))
          m))
      (dissoc* m k))))


(dissoc-in {} [:a :b])
;; => {}
(dissoc-in {:a {}} [:a :b])
;; => {:a {}}
(dissoc-in {:a {:b 1}} [:a :b])
;; => {:a {}}
(dissoc-in {:a [{:b 1}]} [:a 0 :b])
;; => {:a [{}]}
(dissoc-in {:a [{:b [:c :d]}]} [:a 0 :b 0]);; => {:a [{:b [:d]}]}