anchor.diff:          (GuiCnt == 0) ->
               %% (re)initialize buffer
               serve_bot(SN,<<"">>,State0);
  +        (GuiBot == BufBot) andalso (SN == completed) ->
  +            serve_bot(SN,<<>>,State0);
           true ->
               NewGuiBot = key_times_2(GuiBot,State0),
  -            if 
  -                (Nav == ind) andalso (NewGuiBot == undefined) -> 
  +            if
  +                (Nav == ind) andalso (NewGuiBot == undefined) andalso (SN == completed) ->
  +                    serve_bot(SN,<<>>,State0);
  +                (Nav == ind) andalso (NewGuiBot == undefined) ->
                       %% jump leads outside of index table, target double buffer size
                       State1 = prefetch(SN,State0),
                       ?Debug("~p stack ~p", [SN,<<">>">>]),
  
positive.code:             State1 = prefetch(SN,State0),       
              ?Debug("~p stack ~p", [SN,<<"<">>]),
              State1#state{stack={button,<<"<">>,ReplyTo}};
          (GuiTop == BufTop)  ->
              %% we are at the top of the buffer, cannot go backward
              gui_nop(#gres{state=SN,beep=true},State0);
          true ->
  
negative.code: serve_stack(SN, #state{tRef=TRef} = State) when TRef =/= undefined ->
      timer:cancel(TRef),
      serve_stack(SN, State#state{tRef = undefined});
  serve_stack( _, #state{stack=undefined}=State) ->
      % no stack, nothing .. do
      State;
  serve_stack(completed, #state{nav=ind,bufBot=B,guiBot=B,stack={button,Button,RT}}=State0) when
        Button =:= <<">">>;
        Button =:= <<">>">>;
        Button =:= <<">|">>;
  