anchor.diff:  %% @end
   %%-------------------------------------------------------------------------
   
  +-spec fetch_keys(Node :: trie()) -> list(string()).
  +
   fetch_keys(Node) ->
       foldr(fun(Key, _, L) -> [Key | L] end, [], Node).
   
  
positive.code: %% @end
  %%-------------------------------------------------------------------------
  
  find([H | _], {I0, I1, _})
      when H < I0; H > I1 ->
      error;
  
negative.code: %% @end
  %%-------------------------------------------------------------------------
  
  -spec to_list(Node :: trie()) -> list({string(), any()}).
  
  to_list([]) ->
      [];
  
  to_list(Node) ->
      to_list_node([], [], Node).
  
  