(defn with-propagation0
  [sign opts field includer]
  (if-let [outer (sign opts)]
    (if-let [inner (outer (keyword field))]
      (let [down (assoc opts sign inner)]
        (includer down)))))

(defn with-propagation1
  "if (-> nest0 selector-1 (keyword selector-2)),
calls action on nest0 with the key selector1 bound to the binding of selector2
within the previous value of selector1"
  [selector-1 nest-0 selector-2 action]
  (when-let [nest-1 (selector-1 nest-0)]
    (when-let [nest-2 (nest-1 (keyword selector-2))]
      (let [down (assoc nest-0 selector-1 nest-2)]
        (action down)))))

(defn with-propagation2
  [selector-1 nest selector-2 action]
  (when-let [nest-1 (-> nest selector-1 ((keyword selector-2)))]
    (let [nest (assoc nest selector-1 nest-1)]
      (action nest))))