anchor.diff:              State1 = prefetch(SN,State0),       
               ?Debug("~p stack ~p", [SN,<<"<">>]),
               State1#state{stack={button,<<"<">>,ReplyTo}};
  -        (GuiTop == BufTop)  ->
  +        (GuiTop == BufTop) ->
               %% we are at the top of the buffer, cannot go backward
               gui_nop(#gres{state=SN,beep=true},State0);
           true ->
  
positive.code:         (GuiCnt == 0) ->
              %% (re)initialize buffer
              serve_bot(SN,<<"">>,State0);
          true ->
              NewGuiBot = key_times_2(GuiBot,State0),
              if 
                  (Nav == ind) andalso (NewGuiBot == undefined) -> 
                      %% jump leads outside of index table, target double buffer size
                      State1 = prefetch(SN,State0),
                      ?Debug("~p stack ~p", [SN,<<">>">>]),
  
negative.code:                     %% requested jump is possible within existing buffer, do it
                      gui_replace_until(NewGuiBot,BL,#gres{state=SN},State0);
                  (Nav == raw) andalso (SN == filling) ->
                      %% jump is not possible in existing buffer, target
                      State1 = prefetch(SN,State0),
                      ?Debug("~p stack ~p", [SN,NewGuiBot]),
                      State1#state{stack={button,NewGuiBot,ReplyTo}};
  