anchor.diff:  %%   where `Tree' is composed of :
   %%   - {KeyNo, IsLeaf, [{Key, Value}], [Tree]}.
   
  +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  +%% Some macros.
  +
  +-define(B_TREE_EMPTY, {_, _, _, 0, nil}).
  +
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   %% Some types.
   
  
positive.code: 
  -spec is_empty(b_tree()) -> boolean().
  
  is_empty({_, _, _, 0, nil}) ->
      true;
  is_empty(_) ->
      false.
  
negative.code: -spec from_dict(pos_integer(), atom(), key_values()) -> b_tree().
  
  from_dict(Order, KeyValues) when Order > 3, length(KeyValues) > 0 ->
      from_dict_1(KeyValues, empty(Order)).
  from_dict(Order, b_star, KeyValues) when Order > 3, length(KeyValues) > 0 ->
      from_dict_1(KeyValues, empty(Order, b_star)).
  
  -spec from_dict_1(key_values(), b_tree()) -> b_tree().
  
  