anchor.diff:  ;; => 15
   ----
   
  -And the same operation can be done using the `foldr`:
  +And the same operation can be done using `foldr`:
   
   [source, clojure]
   ----
  
positive.code: ;; => 15
  ----
  
  The main difference between `foldl` and `reduce` is that `foldl` has fixed arity so all
  parameters are mandatory and `foldl` is a generic abstraction that can work
  with other types apart from collections.
  
  As we said previously, the `foldl` and `foldr` differs mainly on how they traverse the
  data structure. Then, for better understanding how they works internally, let see a
  graphical representation of the `foldl` execution model:
  
  [source, text]
  
negative.code: ;; => 15
  ----
  
  You can observe that `foldl` is identical to the clojure `reduce` function:
  
  [source, clojure]
  ----
  