How can I write a subscription from another two subs and also get db ? Smth like that:

(rf/reg-sub
  :editor/dataset-schema

  :<- [:db] ;; How to get app state db? 
  :<- [:a] ;; another 2 subs :a and :b
  :<- [:b]    

  (fn [[db a b] _] 

   ))