anchor.diff:      if 
   	NecessaryNofVirtualCols > NofVirtualCols ->
   	    TailNo = NofVirtualCols - FirstColShown + 1,   % Always >= 0 !!!
  -	    NewColWidths ++ lists:nthtail(TailNo, ColsShown);
  +	    NewColWidths ++ safe_nthtail(TailNo, ColsShown);
   	true ->
   	    NewColWidths
       end.
  
positive.code: 
         % Update the ColWidths list.
      TempColWidths = lists:sublist(ColWidths, VirtualCol - 1) ++ 
  	[NewWidthOfCol | lists:nthtail(VirtualCol, ColWidths)],
      
         % Check the other columns, whether a new column has to be created.
      ColsShown    = compute_cols_shown(FirstColShown, TempColWidths, GridWidth, 
  
negative.code: 	check_nof_cols(ColsShown, (NofColsShown - NofCols), ColFrameIds, ColIds, 
  		       RowIds, NofRows, RowHeight, FgColor, BgColor ),
  
      clear_fields(safe_nthtail(NofColsShown, NewColIds),
  		 safe_nthtail(NofRowsShown, NewRowIds)),
  
      RowsToUpdate = lists:sublist(NewRowIds, NofRowsShown),
  
  