anchor.diff:  [source, clojure]
   ----
   (require '[cats.core :as m])
  +(require '[cats.builtin])
   (require '[cats.monad.maybe :as maybe])
   
   (m/mappend (maybe/just [1 2 3])
  
positive.code: [source, clojure]
  ----
  (require '[cats.core :as m])
  
  (m/mappend [1 2 3] [4 5 6])
  ;; => [1 2 3 4 5 6]
  
negative.code: [source, clojure]
  ----
  (require '[cats.core :as m])
  (require '[cats.builtin])
  (require '[cats.monad.maybe :as maybe])
  
  (m/mappend (maybe/just [1 2 3])
  