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 change_cell([cell()], pos_integer(), Key::binary(), value(), cell_operation()) -> [cell()].
  change_cell(Column, CellNr, Key, Value, Operation) ->
      {HeadL, [Cell | TailL]} = lists:split(CellNr, Column),
      {Count, KeySum, KHSum, ValSum, VHSum} = Cell,
      lists:flatten([HeadL, 
                     {Count + operation_val(Operation), 
                      util:bin_xor(KeySum, Key), KHSum bxor checksum_fun(Key),
                      ValSum bxor Value, VHSum bxor checksum_fun(Value)}, 
                     TailL]).
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  