anchor.diff:  		new(link, create(data));
   		if empty() then
   		begin
  -			writeln('empty');
   			m_begin := list_iterator.create(link);
   			m_begin.getLink()^.setNext(m_end.getLink());
   			m_end.getLink()^.setPrev(m_begin.getLink());
  
positive.code: 	end;
  
  	function list.get_begin(): list_iterator;
  	begin
  		get_begin := m_begin;
  	end;
  
  	function list.get_end(): list_iterator;
  	begin
  		get_end := m_end;
  	end;
  
  	procedure list.push_back(data: longInt);
  	begin
  		insert(m_end, data);
  	end;
  
  	function list.pop_back(): longInt;
  
negative.code: 		it: list_iterator;
  		tmp: longInt;
  	begin
  		it := get_end();
  		it.prev();
  		tmp := it.get_data();
  		erase(it);
  