anchor.diff:  %%-------------------------------------------------------------------------
   %% @doc
   %% ===Fold a function over the trie in reverse.===
  +%% Traverses in reverse alphabetical order.
   %% @end
   %%-------------------------------------------------------------------------
   
  
positive.code:          fold/3,
           foldl/3,
           foldr/3,
           from_list/1,
           is_key/2,
           map/2,
           merge/3,
           new/0,
  
negative.code:      {"ab",5},
       {"aba",6},
       {"ammmmmmm",7}] = trie:to_list(trie:from_list(trie:to_list(RootNode4))),
      Liter =  ["aa", "aaa", "aaaaaaaa", "aaaaaaaaaaa", "ab", "aba"],
      Fiter = fun(Key, _, Iter) ->
          case lists:member(Key, Liter) of
              true ->
                  Iter();
              false ->
                  done
          end
      end,
      Fitera = fun
          (_, _, [], _) ->
              done;
          (Key, _, [Key | T], Iter) ->
              Iter(T)
      end,
      ok = trie:iter(Fiter, RootNode4),
      done = trie:itera(Fitera, Liter, RootNode4),
      % trie:map happens to go through in reverse order
      ["aa",
       "aaa",
  