anchor.diff:  -spec is_pure(cell()) -> boolean().
   is_pure({Count, Key, KeyCheck, Val, ValCheck}) ->
       (Count =:= 1 orelse Count =:= -1) andalso
  -        ?Check_sum_fun(Key) =:= KeyCheck andalso
  -        ?Check_sum_fun(Val) =:= ValCheck.
  +        checksum_fun(Key) =:= KeyCheck andalso
  +        checksum_fun(Val) =:= ValCheck.
   
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   
  
positive.code: %% helpers
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  % @doc Increases Val until Val rem Div == 0.
  -spec resize(pos_integer(), pos_integer()) -> pos_integer().
  resize(Val, Div) when Val rem Div == 0 -> 
  
negative.code: 
  -spec encode_key(?RT:key()) -> integer().
  encode_key(Key) ->
      term_to_binary(Key).
  
  -spec decode_key(binary()) -> ?RT:key().
  decode_key(BinKey) ->
      binary_to_term(BinKey).
  