anchor.diff:  %%      matching.
   -spec call_subscribers(State::db(), Operation::close_db | subscr_op_t()) -> db().
   call_subscribers(State = {_DB, Subscr, _SnapState}, Operation) ->
  -    {NewState, _Op} =?DB:foldl(Subscr,
  +    {NewState, _Op} = ?DB:foldl(Subscr,
                 fun call_subscribers_iter/2,
                 {State, Operation}),
       NewState.
  
positive.code:         [{interval, LBr, L, R, RBr} | Tail] -> 
              case intervals:in(StartId, intervals:new(LBr, L, R, RBr)) of
                  true ->
                      [{interval, '[', StartId, R, RBr}] ++ Tail ++ Before ++
                      [{interval, LBr, L, StartId, ')'}];
                  _ ->
                      After ++ Before
              end
  
negative.code:     %% the interval covered by chunk is either the biggest key left of startid
      %% or if there are no keys left of startid simply the biggest key in chunk
      {Left, Right} = lists:splitwith(fun({Key, _, _, _, _}) -> Key < StartId end,
                                      Chunk),
      Last = case Left of
          [] ->
              element(1, lists:max(Right));
          [_|_] ->
              element(1, lists:max(Left))
      end,
      ?TRACE_CHUNK("left: ~p~nright: ~p~ncalc_remaining:~n~p~nNext is ~p minus ~p",
                   [Left, Right, Chunk, Interval, intervals:new('[', StartId, Last, ']')]),
  